My feeling here is that this issue is to do with the custom skin
Zero - I say this because there is a warning in the ACP that a template is outdated, and looking at the coding it has all of the top bar in it.
I can see you were doing a lot of editing of the templates around the sort of time this issue came along too.
Why it isn't affecting all users however, i am unsure of. Possibly my cache being old?