If this is still happening to you right now - We think this issue is caused by something on the sidebar. Could you check your sidebar alerts and/or friend feed (if that's on your sidebar) and see if you can find what's causing it there? You might notice the font size being correct until a certain event?

There was a forum group ping that caused this a few days ago. An attempted fix was deployed. I am curious if it's that event (it wouldn't be fixed retroactively) or if it's something else.