Self-explanatory title, I think.
Example here: https://stackoverflow.com/posts/21689452/revisions
FYI Firefox 26.0 Win XP SP3.
Fixed with a Ctrl+F5 (in both FF26 and IE8, the two browsers I happened to have to hand, and in both of which I witnessed the problem).
Shoddy dependency cache management combined with an adjusted stylesheet?
This still implies the bug would affect other people.