[Reg->5.12.6] Crash when showing a hidden dialog with size grip again on Secondary Monitor

Whan a dialog has been created on a primiary screen and then moved to secondory monitor and then closed. Application crashes if closed dialog is shown again.

Attached example reproduces it with following steps:
Run the application
show the dilaog with button press
move the dialog to second monitor and then close it.
Try to show dialog again from application on primary monitor.

This does not happen if dialog->setSizeGripEnabled(true); is removed. This works good with 5.12.5