Tiled becomes confusing when opened multi tmx file

Bugs
1

Version: Tiled 1.3.0beta
Reproduce step:

  1. Open Tiled, Show Console windows.
  2. Open more than 30 tmx files.
  3. modify every one.
  4. Close one by one, and choose “Don’t save”.
  5. After many, Console will show error:
    qt.qpa.window: Window position QRect(1519,425 100x30) outside any known screen, using primary screen.
  6. The confirm dialog will not be in the right place.