Amazing how venting a little spleen can solve problems.
I created a second instance of the Time record file and set up a relationship to the second instance of the Jobs list file.
That bypassed the ID relationship and now the menu works fine on the Job ID field.
One other option is to create a stored calculation field, that if the job is Active, stores the job ID/number. Then, create a value list based on that calculated field. No joins or relationships necessary.
Well, actually I would still need the original ID relationship since the field is in a separate file (upgraded from Filemaker 6 and havent got around to merging into one file yet).
Anyway, your solution is much simpler and hence less likely to break.