I previously builded my own Data model with single entity type with the first key assignment type as the tutorial [Develop a Custom Master Data Object]. By using USMD_ENTITY_VALUE2 the UI seems fine (I tried USMD_OVP_GEN but didn't work for me).
Now I changed the key assignment to "key can be changed, internal key assignment", then active the data model, create change request, etc. The UI shows "500 SAP Internal Server Error, The ASSERT condition was violated. termination: RABAX_STATE".
Am I supposed to do anything else to make my custom data model generates the key just as MM - assign a temporary key when change request creates.