Interesting, a font size of 10 is significant when replicating this bug. When I use a size of 12, no change in the field height occurs. (Using XP for this test.)
Thanks for posting!
I was able to reproduce this behavior when the field is set to a font size of 9 or 10. I also confirmed that this does not occur on OS X at all. I've forwarded your post to our Development and Quality Assurance (testing) departments for further investigation.