I'm not sure why this is happening. I made a quick example workbook that shows what I think you are going for and it is attached.
It may be something having to do with your view that I can't see from your question. If the problem persists, would you please attached a workbook so we can see what's going on and help out more? Here's a tutorial: Attaching a Packaged Workbook
Hope this helps!
Calculated Field - BY.twbx 21.3 KB