Inherit from a QDialog, after executing exec, the dialog is displayed again in multiple screens, and the window crashes

1) New a class inherited from dialog (no inheritance and dialog seem to be OK)
2) Exec in button slot function
3) Click window close to execute dialog close
4) Two computer screens, drag the displayed dialog to another screen (it must be multi screen, single screen is OK)
5) Click the button again to execute exec in the slot function

Collapse. It can reappear stably. I gave an example in the attachment.
sorry my poor english . i code for example

1) class test public :Qdialog
2) test * p1 = new test
3) in a button slot function : p1->exec()
4) close dialog 

5) drag main windows to another computer screens
6) click button then slot function: p1->exec() again
7) now you see bug