Datastore layer still not editable after the source has been detached

[mukoki]

Create a datastore layer from a postgresql database table.
Make it editable : a message is warning the user that the layer is not editable and that he can detach the datasource to be able to modify the layer
If the user answer yes, the datasource is detached (visible from the metadata) but the layer is in a strange state where the user can edit it (delete features, move points etc) but edit operations are completely ignored

[mukoki]

More precisely : the problem only arises with the "not in memory" option of the datastore layer.
It seems that when the user accept to detach the source, the source is removed from metadata, but it is still referenced in the layer.