Possible Duplicate:
Going back after voting shows the page without my vote in Chrome
When I upvote/downvote, then click edit on the question to either see what the edit was or to edit it myself, only to back out by clicking the back button, my upvote/downvote disappears. If you refresh/reload the page, the upvote/downvote is back, as it should be.
** Note that I've only tested this in Chrome 10 **