QWS doesn't always handle popup mouse events properly

I have reproduced this behaviour and I think there is something wrong with
Qt::Popup flag on qws. I attach the example. To reproduce:
1) Click "Popup panel"
2) Click "Menu" button
3) When popup menu with months is visible click "Other button" - on qws
handling goes to that button (putton interacts) and month popup is not closed
(while on x11 it just causes the month popup to disappear and handling
doesn't go the the "Other button").

See task 138361 - maybe this is related