Data Architect Issue: Missing PKs for associative entities. Fully baffled, afraid it's obvious

Weird DA issue, running on 17.1 version. 

Two entities in the model entity "A" and entity "B".   Trying to create an associative entity between them.   I create "Association 1"  I then create an identifying relationship between "A" and "Association 1"  The PK for "A" shows up as a PK/FK in "A", so far so good.  I then create a relationship between "B" and "Association 1".   PK from "B" does not show up in the "Association 1" Entity in any way.  The key to "B" does not show up as an attribute, it does show up as an FK in the relationships tab for the "Association 1" entity.   Trying to add the attribute in the entity flags that it can't be added.   This type of entity works for every other combo of entities and relationships in the model.  I am baffled.  Any thoughts.