I would really have to play with it to test out stuff, but you might want to create another calc in the primary data source that has 4 values -- 1,2,3,4 -- based on the quarter, and see if using that would help. (Use the DATEPART() function to grab quarter.) Maybe the problem is that quarter is part of a date hierarchy, and that might be what's messing you up.
I have used multiple fields from multiple secondary data sources in calcs, so that's not the problem here.
If you want to hack up a sample workbook that we can play with together, consider simulating your data in an excel file with three sheets. Create enough rows to simulate the behavior you are looking to achieve.