This bug may related to:
QTBUG-40681 [REG 4->5] When using multiple monitors and one monitor is disconnected causing the window to move then winId() is not updated - Qt Bug Tracker
QTBUG-40771 Add QEvent::WinIdAboutToBeChanged event to QWidget - Qt Bug Tracker
I am using Calibre 2.2 (an ebook management system) which uses Qt 5.3.1 at an Ubuntu 14.04 system.
I am using a KVM switch, some times, if i switch away from the Ubuntu system, Calibre crashed with a Segmentation fault (core dumped).
I gave the developer a back trace and he said, it is a bug in Qt 5.3.1.
You can habe a look in the calibre issue here: