I first noticed this in the review queue on the main site, but it also occurs on both the main site and the meta site when asking a question.
Main site, review queue
Meta site, asking a new question
Is this a bug, or something peculiar to my setup? Can anyone reproduce this? It appears in both Iceweasel 17.0.8 and Chromium 29.0.1547.57, the only browsers I have access to at the moment, on my x64 Debian system. The old version of Iceweasel may not be a supported browser, but I believe this version of Chromium is supported.
My browsers are using all the default settings (zoom, etc.), as far as I know. I didn't notice this on the few other sites I checked, e.g. webapps.SE, SO, money.SE, etc. (sites where I'm active, basically).