I would really like to see this reproduced on some other machine. So far I have only seen this happen on Stefans.
Confirmed on Mac OS X 10.9, Qt 4.8.6.
See attached screenshot (the Close project pop-up window). The same holds for the 'Quit' entry in the File Menu.
So far I have not managed to reproduce this issue on either windows or linux. You are both using Qt 4.8.6 ? Does the issue appear in Release and Debug?
Wy windows is using 4.8.1