I've got a little niggle with a project I'm working on at the moment - when I make an anchor .resizable() which is also positioned : absolute and resize from left or top handles, the elements shifts a couple of pixels.
I thought the borders were the culprit, but when taken off, it still nudges 1 pixel along on each resize.
It appears that the bug only occurs if you use a helper. My updated jsFiddle doesn't have the buggy behavior. This would suggest that it is a bug in jQueryUI and it might be worthwhile filing a bug report with them and posting the ticket here.