Adapt UW to account for the change in jQuery's behaviour since jQuery 1.5.2. jQuery attempts to interact with the API by passing a callback parameter (to avoid having to parse JSON strings which is likely slower than just calling a callback).
Since the API assumes the origin to be an anonymous user if the callback-parameter is passed we have to override this when dealing with the API (since uploading requires the user to be logged in).
Setting jsonp:false will do this. See also:
http://api.jquery.com/jQuery.ajax/ (scroll to "jsonp" setting and the note about jQuery 1.5)
(Follow-up
r88607: Upgrade jQuery 1.4.4 to 1.5.2)