QPrintPreviewWidget and QPrintPreviewDialog hang when in page width zoom mode and view is sized just about where it needs a vertical scrollbar.
To reproduce, build and run the TextEdit demo, delete most of the demo text so there is only one page. Open the print preview. Press the page width zoom button. Then size the window just to the point where the vertical scroll bar is required. You might have to tweak back and forth a few times to hit the bug.
It appears that the code enters an endless loop resizing with and without the scroll bar.