Random Font size changing in Excel 2007

I'm hoping that I'm not being too terribly ignorant, and that there's just something funky going on that's easy to fix. Here's the problem:

I've set up an Excel worksheet that is being used as a database, version 2007, and it's being shared between several people. Some of us have noticed that their font size has been changing after they've entered some text into a cell. That is, a cell will have information already in it, someone will enter something additional and everything is fine (ie. font size), then some time later they'll go back and notice that the info they've just entered has changed in size, but the earlier text is still in the original size. We had some earlier problems arising from the autocalculate function, but have since turned that off and it's still happening.

Sorry for the roundabout explanation, hope someone can help shed some light.

JP

Can you post this workbook or at least a dummy version of it? Thanks.