If a QDialog is repeatedly executed (using QDialog::exec()) the dialog will change size and/or move its position. I've attached a couple screenshots and a minimal example application that illustrates this issue. To duplicate:

1. Unzip and compile the attached project inside qdialogMoves.zip
2. Launch application and press the Show Dialog button (screenshot below shows the result the first time the button is pressed)
3. 
   1. Observe size and location of initial dialog
   2. Close dialog using the 'X' in the upper right corner
4. Repeat step #2 multiple times, observing how the dialog changes its size/position. Screenshot below shows after the 21st time:
5. 

At no point am I intentionally resizing the dialog - neither via the mouse nor programmatically using resize() for example.

I've also attached a video showing the behavior in real time.