Maybe you should do a comparison of the fonts in you "clean" users Fonts folder, and in the Fonts folder of your affected account. If there is a font (or more than one) that is in the first account and not the latter, that may be the problem.
However, I come to think that if there were a real problem, the characters wouldn't show up at all, or at least not properly. Are you running any Haxies, or could this be connected to a Tinkertool setting or something?