diff --git a/op2/src/core/op_lib_core.cpp b/op2/src/core/op_lib_core.cpp
index 265107436..a5ef2199c 100644
--- a/op2/src/core/op_lib_core.cpp
+++ b/op2/src/core/op_lib_core.cpp
@@ -476,13 +476,15 @@ op_dat op_decl_dat_core(op_set set, int dim, char const *type, int size,
       memcpy(new_data, data, (size_t)dim * (size_t)size * (size_t)set->size * sizeof(char));
 
     dat->data = new_data;
-  }
-  else {
-    if (data != NULL)
+    dat->user_managed = 0;
+  } else {
+    if (data != NULL) {
       dat->data = data;
-    else {
-      char *new_data = (char *)op_malloc(bytes);
+      dat->user_managed = 1;
+    } else {
+      char *new_data = (char *)op_calloc(bytes, sizeof(char));
       dat->data = new_data;
+      dat->user_managed = 0;
     }
   }
 
@@ -490,7 +492,6 @@ op_dat op_decl_dat_core(op_set set, int dim, char const *type, int size,
   dat->name = copy_str(name);
   dat->type = copy_str(type);
   dat->size = dim * size;
-  dat->user_managed = 1;
   dat->mpi_buffer = NULL;
   dat->buffer_d = NULL;
   dat->buffer_d_r = NULL;
@@ -508,14 +509,13 @@ op_dat op_decl_dat_core(op_set set, int dim, char const *type, int size,
     exit(-1);
   }
   item->dat = dat;
-  /*if (data == NULL) { -- this check would be good to have for Hydra,
-                           but temp_dats prints this error .. so commented out
-  for now
-    printf("WARNING data pointer is NULL for %s!\n", name);
-  }*/
-  item->orig_ptr = data;
-  // printf("orig_ptr for dat %s = %p\n", name, data);
-  // add item to the end of the list
+
+  if (data != NULL) {
+    item->orig_ptr = data;
+  } else {
+    item->orig_ptr = dat->data;
+  }
+
   if (TAILQ_EMPTY(&OP_dat_list)) {
     TAILQ_INSERT_HEAD(&OP_dat_list, item, entries);
   } else {
@@ -1313,7 +1313,8 @@ void set_maps_base(int base) {
 }
 
 void *op_malloc(size_t size) {
-  return aligned_alloc(OP2_ALIGNMENT, size);
+  if (size == 0) return malloc(0);
+  return aligned_alloc(OP2_ALIGNMENT, (size + OP2_ALIGNMENT) - 1 & (-OP2_ALIGNMENT));
 }
 
 // malloc to be exposed in Fortran API for use with Cray pointers
diff --git a/op2/src/cuda/op_cuda_decl.cpp b/op2/src/cuda/op_cuda_decl.cpp
index f6dd09d2b..3f6b4b98c 100644
--- a/op2/src/cuda/op_cuda_decl.cpp
+++ b/op2/src/cuda/op_cuda_decl.cpp
@@ -122,23 +122,7 @@ op_dat op_decl_dat_overlay_ptr(op_set set, char *dat) {
 
 op_dat op_decl_dat_temp_char(op_set set, int dim, char const *type, int size,
                              char const *name) {
-  char *data = NULL;
-  op_dat dat = op_decl_dat_temp_core(set, dim, type, size, data, name);
-
-  op_dat_entry *item;
-  op_dat_entry *tmp_item;
-  for (item = TAILQ_FIRST(&OP_dat_list); item != NULL; item = tmp_item) {
-    tmp_item = TAILQ_NEXT(item, entries);
-
-    if (item->dat == dat) {
-      item->orig_ptr = (char *)dat->data;
-      break;
-    }
-  }
-
-  for (size_t i = 0; i < set->size * dim * size; i++)
-    dat->data[i] = 0;
-  dat->user_managed = 0;
+  op_dat dat = op_decl_dat_temp_core(set, dim, type, size, NULL, name);
 
   size_t set_size = dat->set->size + dat->set->exec_size + dat->set->nonexec_size;
   if (strstr(dat->type, ":soa") != NULL || (OP_auto_soa && dat->dim > 1)) {
@@ -149,7 +133,6 @@ op_dat op_decl_dat_temp_char(op_set set, int dim, char const *type, int size,
     op_deviceZero(dat->data_d, (size_t)(dat->size) * set_size);
   }
 
-
   return dat;
 }
 
diff --git a/op2/src/mpi/op_mpi_cuda_decl.cpp b/op2/src/mpi/op_mpi_cuda_decl.cpp
index cf25d522f..ed20b8bee 100644
--- a/op2/src/mpi/op_mpi_cuda_decl.cpp
+++ b/op2/src/mpi/op_mpi_cuda_decl.cpp
@@ -119,16 +119,16 @@ op_dat op_decl_dat_char(op_set set, int dim, char const *type, int size,
 op_dat op_decl_dat_overlay(op_set set, op_dat dat) {
   op_dat overlay_dat = op_decl_dat_overlay_core(set, dat);
 
-  int halo_size = OP_import_exec_list[set->index]->size +
-                  OP_import_nonexec_list[set->index]->size;
-
   op_mpi_buffer mpi_buf = (op_mpi_buffer)xmalloc(sizeof(op_mpi_buffer_core));
 
   halo_list exec_e_list = OP_export_exec_list[set->index];
   halo_list nonexec_e_list = OP_export_nonexec_list[set->index];
 
-  mpi_buf->buf_exec = (char *)xmalloc((exec_e_list->size) * overlay_dat->size);
-  mpi_buf->buf_nonexec = (char *)xmalloc((nonexec_e_list->size) * overlay_dat->size);
+  mpi_buf->buf_exec = (char *)xmalloc((size_t)(exec_e_list->size) * (size_t)overlay_dat->size);
+
+  size_t import_extra = OP_partial_exchange ? set_import_buffer_size[set->index] : 0;
+  mpi_buf->buf_nonexec = (char *)xmalloc(((size_t)(nonexec_e_list->size) + import_extra)
+                                         * (size_t)overlay_dat->size);
 
   halo_list exec_i_list = OP_import_exec_list[set->index];
   halo_list nonexec_i_list = OP_import_nonexec_list[set->index];
@@ -170,37 +170,19 @@ op_dat op_decl_dat_overlay_ptr(op_set set, char *dat) {
 
 op_dat op_decl_dat_temp_char(op_set set, int dim, char const *type, int size,
                              char const *name) {
-  char *data = NULL;
-  op_dat dat = op_decl_dat_temp_core(set, dim, type, size, data, name);
-
-  op_dat_entry *item;
-  op_dat_entry *tmp_item;
-  for (item = TAILQ_FIRST(&OP_dat_list); item != NULL; item = tmp_item) {
-    tmp_item = TAILQ_NEXT(item, entries);
-
-    if (item->dat == dat) {
-      item->orig_ptr = (char *)dat->data;
-      break;
-    }
-  }
+  op_dat dat = op_decl_dat_temp_core(set, dim, type, size, NULL, name);
 
   // create empty data block to assign to this temporary dat (including the
   // halos)
-  size_t set_size = (size_t)set->size + (size_t)OP_import_exec_list[set->index]->size +
-                    (size_t)OP_import_nonexec_list[set->index]->size;
-
-  // initialize data bits to 0
-  for (size_t i = 0; i < set_size * (size_t)dim * (size_t)size; i++)
-    dat->data[i] = 0;
-
-  dat->user_managed = 0;
+  size_t set_size = (size_t)set->size + (size_t)OP_import_exec_list[set->index]->size
+                                      + (size_t)OP_import_nonexec_list[set->index]->size;
 
   // transpose
   if (strstr(dat->type, ":soa") != NULL || (OP_auto_soa && dat->dim > 1)) {
     cutilSafeCall(
         op_deviceMalloc((void **)&(dat->buffer_d_r),
-                   (size_t)dat->size * (OP_import_exec_list[set->index]->size +
-                                OP_import_nonexec_list[set->index]->size)));
+                   (size_t)dat->size * ((size_t)OP_import_exec_list[set->index]->size +
+                                        (size_t)OP_import_nonexec_list[set->index]->size)));
 
     op_deviceMalloc((void **)&(dat->data_d), (size_t)(dat->size) * round32(set_size));
     op_deviceZero(dat->data_d, (size_t)(dat->size) * round32(set_size));
@@ -212,14 +194,16 @@ op_dat op_decl_dat_temp_char(op_set set, int dim, char const *type, int size,
   // need to allocate mpi_buffers for this new temp_dat
   op_mpi_buffer mpi_buf = (op_mpi_buffer)xmalloc(sizeof(op_mpi_buffer_core));
 
-  halo_list exec_e_list = OP_export_exec_list[set->index];
-  halo_list nonexec_e_list = OP_export_nonexec_list[set->index];
+  halo_list exec_e_list = OP_export_exec_list[dat->set->index];
+  halo_list nonexec_e_list = OP_export_nonexec_list[dat->set->index];
 
-  mpi_buf->buf_exec = (char *)xmalloc((exec_e_list->size) * (size_t)dat->size);
-  mpi_buf->buf_nonexec = (char *)xmalloc((nonexec_e_list->size) * (size_t)dat->size);
+  mpi_buf->buf_exec = (char *)xmalloc((size_t)(exec_e_list->size) * (size_t)dat->size);
 
-  halo_list exec_i_list = OP_import_exec_list[set->index];
-  halo_list nonexec_i_list = OP_import_nonexec_list[set->index];
+  size_t import_extra = OP_partial_exchange ? set_import_buffer_size[set->index] : 0;
+  mpi_buf->buf_nonexec = (char *)xmalloc(((size_t)(nonexec_e_list->size) + import_extra) * (size_t)dat->size);
+
+  halo_list exec_i_list = OP_import_exec_list[dat->set->index];
+  halo_list nonexec_i_list = OP_import_nonexec_list[dat->set->index];
 
   mpi_buf->s_req = (MPI_Request *)xmalloc(
       sizeof(MPI_Request) *
@@ -230,14 +214,13 @@ op_dat op_decl_dat_temp_char(op_set set, int dim, char const *type, int size,
 
   mpi_buf->s_num_req = 0;
   mpi_buf->r_num_req = 0;
-
   dat->mpi_buffer = mpi_buf;
 
   // need to allocate device buffers for mpi comms for this new temp_dat
-  cutilSafeCall(
-      op_deviceMalloc((void **)&(dat->buffer_d),
-                 (size_t)dat->size * (OP_export_exec_list[set->index]->size +
-                              OP_export_nonexec_list[set->index]->size)));
+  cutilSafeCall(op_deviceMalloc((void **)&(dat->buffer_d),
+      (size_t)dat->size * (OP_export_exec_list[set->index]->size +
+                           OP_export_nonexec_list[set->index]->size +
+                           set_import_buffer_size[set->index])));
 
   return dat;
 }
@@ -288,7 +271,7 @@ size_t op_mv_halo_device(op_set set, op_dat dat) {
     cutilSafeCall(
         op_deviceMalloc((void **)&(dat->buffer_d_r),
                    (size_t)dat->size * (OP_import_exec_list[set->index]->size +
-                                OP_import_nonexec_list[set->index]->size)));
+                                        OP_import_nonexec_list[set->index]->size)));
 
     total_size += (size_t)dat->size * (OP_import_exec_list[set->index]->size +
                                        OP_import_nonexec_list[set->index]->size);
@@ -304,8 +287,8 @@ size_t op_mv_halo_device(op_set set, op_dat dat) {
   cutilSafeCall(
       op_deviceMalloc((void **)&(dat->buffer_d),
                  (size_t)dat->size * (OP_export_exec_list[set->index]->size +
-                              OP_export_nonexec_list[set->index]->size +
-                              set_import_buffer_size[set->index])));
+                                      OP_export_nonexec_list[set->index]->size +
+                                      set_import_buffer_size[set->index])));
 
   total_size += (size_t)dat->size * (OP_export_exec_list[set->index]->size +
                                      OP_export_nonexec_list[set->index]->size +
diff --git a/op2/src/mpi/op_mpi_decl.cpp b/op2/src/mpi/op_mpi_decl.cpp
index 59b243335..b8232ee4d 100644
--- a/op2/src/mpi/op_mpi_decl.cpp
+++ b/op2/src/mpi/op_mpi_decl.cpp
@@ -132,8 +132,11 @@ op_dat op_decl_dat_overlay(op_set set, op_dat dat) {
   halo_list exec_e_list = OP_export_exec_list[set->index];
   halo_list nonexec_e_list = OP_export_nonexec_list[set->index];
 
-  mpi_buf->buf_exec = (char *)xmalloc((exec_e_list->size) * overlay_dat->size);
-  mpi_buf->buf_nonexec = (char *)xmalloc((nonexec_e_list->size) * overlay_dat->size);
+  mpi_buf->buf_exec = (char *)xmalloc((size_t)(exec_e_list->size) * (size_t)overlay_dat->size);
+
+  size_t import_extra = OP_partial_exchange ? set_import_buffer_size[set->index] : 0;
+  mpi_buf->buf_nonexec = (char *)xmalloc(((size_t)(nonexec_e_list->size) + import_extra)
+                                         * (size_t)overlay_dat->size);
 
   halo_list exec_i_list = OP_import_exec_list[set->index];
   halo_list nonexec_i_list = OP_import_nonexec_list[set->index];
@@ -175,42 +178,26 @@ op_dat op_decl_dat_overlay_ptr(op_set set, char *dat) {
 
 op_dat op_decl_dat_temp_char(op_set set, int dim, char const *type, int size,
                              char const *name) {
-  char *d = NULL;
-  op_dat dat = op_decl_dat_temp_core(set, dim, type, size, d, name);
-
-  op_dat_entry *item;
-  op_dat_entry *tmp_item;
-  for (item = TAILQ_FIRST(&OP_dat_list); item != NULL; item = tmp_item) {
-    tmp_item = TAILQ_NEXT(item, entries);
-
-    if (item->dat == dat) {
-      item->orig_ptr = (char *)dat->data;
-      break;
-    }
-  }
+  op_dat dat = op_decl_dat_temp_core(set, dim, type, size, NULL, name);
 
   // create empty data block to assign to this temporary dat (including the
   // halos)
-  int halo_size = OP_import_exec_list[set->index]->size +
-                  OP_import_nonexec_list[set->index]->size;
-
-  // initialize data bits to 0
-  //dat->data = (char *)calloc((set->size + halo_size) * dim * size, 1);
-  for (size_t i = 0; i < (set->size + halo_size) * dim * size; i++)
-    dat->data[i] = 0;
-  dat->user_managed = 0;
+  size_t set_size = (size_t)set->size + (size_t)OP_import_exec_list[set->index]->size
+                                      + (size_t)OP_import_nonexec_list[set->index]->size;
 
   // need to allocate mpi_buffers for this new temp_dat
   op_mpi_buffer mpi_buf = (op_mpi_buffer)xmalloc(sizeof(op_mpi_buffer_core));
 
-  halo_list exec_e_list = OP_export_exec_list[set->index];
-  halo_list nonexec_e_list = OP_export_nonexec_list[set->index];
+  halo_list exec_e_list = OP_export_exec_list[dat->set->index];
+  halo_list nonexec_e_list = OP_export_nonexec_list[dat->set->index];
 
-  mpi_buf->buf_exec = (char *)xmalloc((exec_e_list->size) * dat->size);
-  mpi_buf->buf_nonexec = (char *)xmalloc((nonexec_e_list->size) * dat->size);
+  mpi_buf->buf_exec = (char *)xmalloc((size_t)(exec_e_list->size) * (size_t)dat->size);
 
-  halo_list exec_i_list = OP_import_exec_list[set->index];
-  halo_list nonexec_i_list = OP_import_nonexec_list[set->index];
+  size_t import_extra = OP_partial_exchange ? set_import_buffer_size[set->index] : 0;
+  mpi_buf->buf_nonexec = (char *)xmalloc(((size_t)(nonexec_e_list->size) + import_extra) * (size_t)dat->size);
+
+  halo_list exec_i_list = OP_import_exec_list[dat->set->index];
+  halo_list nonexec_i_list = OP_import_nonexec_list[dat->set->index];
 
   mpi_buf->s_req = (MPI_Request *)xmalloc(
       sizeof(MPI_Request) *
@@ -221,7 +208,6 @@ op_dat op_decl_dat_temp_char(op_set set, int dim, char const *type, int size,
 
   mpi_buf->s_num_req = 0;
   mpi_buf->r_num_req = 0;
-
   dat->mpi_buffer = mpi_buf;
 
   return dat;
diff --git a/op2/src/openmp/op_openmp_decl.cpp b/op2/src/openmp/op_openmp_decl.cpp
index c846b560f..50da56fda 100644
--- a/op2/src/openmp/op_openmp_decl.cpp
+++ b/op2/src/openmp/op_openmp_decl.cpp
@@ -102,24 +102,7 @@ op_dat op_decl_dat_overlay_ptr(op_set set, char *dat) {
 
 op_dat op_decl_dat_temp_char(op_set set, int dim, char const *type, int size,
                              char const *name) {
-  char *data = NULL;
-  op_dat dat = op_decl_dat_temp_core(set, dim, type, size, data, name);
-
-  op_dat_entry *item;
-  op_dat_entry *tmp_item;
-  for (item = TAILQ_FIRST(&OP_dat_list); item != NULL; item = tmp_item) {
-    tmp_item = TAILQ_NEXT(item, entries);
-
-    if (item->dat == dat) {
-      item->orig_ptr = (char *)dat->data;
-      break;
-    }
-  }
-
-  for (size_t i = 0; i < set->size * dim * size; i++)
-    dat->data[i] = 0;
-  dat->user_managed = 0;
-  return dat;
+  return op_decl_dat_temp_core(set, dim, type, size, NULL, name);
 }
 
 int op_free_dat_temp_char(op_dat dat) { return op_free_dat_temp_core(dat); }
diff --git a/op2/src/openmp4/op_openmp4_decl.cpp b/op2/src/openmp4/op_openmp4_decl.cpp
index 36c4bebf8..7a815575b 100644
--- a/op2/src/openmp4/op_openmp4_decl.cpp
+++ b/op2/src/openmp4/op_openmp4_decl.cpp
@@ -96,23 +96,7 @@ op_dat op_decl_dat_overlay_ptr(op_set set, char *dat) {
 
 op_dat op_decl_dat_temp_char(op_set set, int dim, char const *type, int size,
                              char const *name) {
-  char *data = NULL;
-  op_dat dat = op_decl_dat_temp_core(set, dim, type, size, data, name);
-
-  op_dat_entry *item;
-  op_dat_entry *tmp_item;
-  for (item = TAILQ_FIRST(&OP_dat_list); item != NULL; item = tmp_item) {
-    tmp_item = TAILQ_NEXT(item, entries);
-
-    if (item->dat == dat) {
-      item->orig_ptr = (char *)dat->data;
-      break;
-    }
-  }
-
-  for (size_t i = 0; i < set->size * dim * size; i++)
-    dat->data[i] = 0;
-  dat->user_managed = 0;
+  op_dat dat = op_decl_dat_temp_core(set, dim, type, size, NULL, name);
 
   // transpose data
   if (strstr(type, ":soa") != NULL || (OP_auto_soa && dim > 1)) {
diff --git a/op2/src/sequential/op_seq.cpp b/op2/src/sequential/op_seq.cpp
index 89cf15932..059a5fd9d 100644
--- a/op2/src/sequential/op_seq.cpp
+++ b/op2/src/sequential/op_seq.cpp
@@ -109,24 +109,7 @@ int op_free_dat_temp_char(op_dat dat) { return op_free_dat_temp_core(dat); }
 
 op_dat op_decl_dat_temp_char(op_set set, int dim, char const *type, int size,
                              char const *name) {
-  char *data = NULL;
-  op_dat dat = op_decl_dat_temp_core(set, dim, type, size, data, name);
-
-  op_dat_entry *item;
-  op_dat_entry *tmp_item;
-  for (item = TAILQ_FIRST(&OP_dat_list); item != NULL; item = tmp_item) {
-    tmp_item = TAILQ_NEXT(item, entries);
-
-    if (item->dat == dat) {
-      item->orig_ptr = (char *)dat->data;
-      break;
-    }
-  }
-
-  for (size_t i = 0; i < set->size * dim * size; i++)
-    dat->data[i] = 0;
-  dat->user_managed = 0;
-  return dat;
+  return op_decl_dat_temp_core(set, dim, type, size, NULL, name);
 }
 
 /*