When a QMessageBox is created with setModal(true), the user can in theory choose to show() it, and then return back to the main event loop, instead of calling exec(). We tried to support that case via a single shot timer, called on the next pass of the event loop, that checked if the applications' current modal window was the alert, and if not, showed it at that point. That logic failed when there were more than one alert show at the same time. We do maintain a stack of the modal sessions and their windows in the Cocoa event dispatcher, so we could use that to check if a modal session had been started for the alert's window, but a similar solution is to just check the alert window's visible state. Fixes: QTBUG-121557 Change-Id: I6f52a53e8f678bb8a071e334a09ab30669d95bbf Reviewed-by: Eike Ziller <eike.ziller@qt.io> (cherry picked from commit 7edff3f15ae21c2310437e0711f84442a21cb6a1) Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org> (cherry picked from commit c967ee08c82aef011b319e5efacf5d1269c18e90) (cherry picked from commit 7c782dc20a032a612271341b7a067b9397386502) Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>