On the Recent Activity page (accessible by clicking the envelope icon next to the user's name at the top) (eg. https://ux.stackexchange.com/users/recent/34 ), clicking on the tabs (Summary, Reputation, Responses etc) causes a blank page to appear (400 Bad Request).
This may have to do with the url - on SO the url is of the format https://stackoverflow.com/users/recent/1943?startdate=2010-08-24%2015%3a32%3a27z&enddate=2010-08-24%2023%3a59%3a59z&tab=summary#tab-top
while on ui, it's https://ux.stackexchange.com/users/recent/34/2010-08-24%2014:41:53z/2010-08-24%2023:59:59z?tab=reputation#tab-top ('/' instead of '?' after userid)