It's on todo since about a month:
Quote from changes.txt
[xx] UserProfile Popups are misplaced a lot. It is more annoying to scroll than to clickX. (thx paipai)
The original idea was to allow clicking a username twice to open and close the popup without the need of moving the mouse.
It obviously does not work as intended.
Anyway, thank you for your suggestion / bugreport, it raised the priority here

I will try to fix it as soon as possible.