Setting a cancel button on QProgressDialog more than once causes layout to be invalid

The attached test project demonstrates a bug where, every time after the first show() of a progress dialog, and only if setCancelButton() is called every time before show(), the button is shown at the top-left corner (on top of everything else) instead of (I presume it's normally inside a layout) at the bottom-right.

Steps to reproduce:

• run attached project
• click test button to show progress dialog
• click cancel button
• click test button again
• cancel button now shows up in the wrong place

Workaround:

Resize the window after it's shown. The cancel button moves to the correct location.

The attached picture "first-show" is what is observed when the test button is clicked once. The "second-show" image is what is seen after clicking the button a second time.