Well, the threads about this beheviour are all over the forums. But one thing always pops up: Mozilla based browser (and not only the new ones). Also, I have seen these same "errors" on other pages on the net as well (which don't use any form of cascade styling; although the errors look the same, it could be something else also though).
IMHO, it has something todo with how the page is loaded by your browser (images first/last, lag on downloading images, etc..., something like that). IF this is a CSS-error which can be fixed, it would be extremely hard/impossible to debug and find the fix. IF this is a Gecko bug, it is a very very very old one, because it also happens with old versions of it (like Netscape 7.0).
I don't think the solution should be found by debugging the Plus!-pages (as this would be almost impossible as the bug can't be reproduced on command), but by searching the web for reports about this...
And in the main time, this is nothing that a simply press on F5 (refresh) can't fix, so...
EDIT1: crap
For only the sake of myself I hope that the bug isn't fixed by removing the </div> or I'm pwnd big time
EDIT2: Patchou, you should try Netscape then (even less buggy (for now... still...))
EDIT3: problem still not fixed it seems...
*phew* 
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