In FM11, I could create a value list that pulls from two fields in different tables and only the values that exist in the first table would show.
For example, I have Contacts and Teachers. A Teacher is a 1:1 child of a Contact record and contains teacher-specific info. I made a value list that pulls the ID from from Teachers to store and the Name from Contacts to display. This gives me a value list of all the teachers.
I converted to 12 and now that value list is showing ALL the Contact records and for non-teachers storing null in the field.