I came across this questionthis question, where I saw this:
It looks like some sort of CSS issue, and it may have to do with the new MathJax 2.3 beta. However, I vaguely recall seeing this type of rendering glitch before -- which is why I didn't post as an answer there.
I used Windows 7 Pro SP1, x64, and Chrome 30.0.x to produce this image.