A tooltip has a maximum width. When the text exceeds that maximum width, it is wrapped. However, for a single very long "word", there is no appropriate behaviour other than to allow the text to overflow its box. This is standard for boxes in HTML.
Your problem would ordinarily be solved simply by giving the QuickTip a larger maximum width. However, I've tried this with your test case and can't quite seem to make it work correctly. I've filed a bug to take a look and figure out what exactly is causing this problem.