timestamp fields dont work in mysql "ERROR Invalid ndc types"

[robthompsonweb]

Given a simple MySql table

CREATE TABLE users(idint unsigned NOT NULL AUTO_INCREMENT,created_at timestamp NULL DEFAULT NULL, PRIMARY KEY (id) )

ddn connector introspect app_mysql and then ddn model add app_mysql chronomics_stage2.users

gives the error
NF Using Subgraph config file "app/subgraph.yaml" found in context. LOAD Subgraph at app/subgraph.yaml UPDATE Model Users in app at app/metadata/Users.hml UPDATE ObjectType Users at app/metadata/Users.hml ERROR Invalid ndc types in app_mysql subgraph app

Take out the timestamp field and it works