So far it's an intermittent problem. I'm mostly using Chrome (41.0 64bit). I've tried it in IE11 and not reproduced it so far. When I do encounter the problem I've found that if I click and drag the login element it keep the pop up open. Going to do some more tests in IE, Opera and Firefox and see if I can work out what is going on. My first thought is that it's simply thinking the mouse has moved onto the blue menu bar rather than the popup div/frame.