Relationship maddness

[ClifG]

Ok so I am not really this dense all the time, But this is driving me nutz.

I have a two file application using separation in that the data tables are in one file and the interface and some logic in the other. Mostly this has worked well, but here is the rub.

When creating calculated fields in a logic table in the Interface file, I am having trouble with the 'Evaluate from' choice. As I understand it, if there is more than one reference to a table in the diagram, they should show up here so that you can choose the correct context. So far so good. I created a few useful calcs then a few days later went back to add some more and the context I was using does not show up as a choice. Other references to the file show up but the one I had used and want to use is not a choice!

I can't see what decides what tables are on this list. What did I do, what am I not doing?