Calling hide(), then show() on a QDialog doesn't correctly preserve its geometry

In Qt5, creating a dialog, then calling hide() and later show() on it would restore it in the same location with the same size.

In Qt6, this behaviour seems broken. On Linux/X11, I get different kinds of broken behaviours, ranging from a correctly sized window with rendering issues to the size just being reset (seems to be random). On Windows, size seems to always be forgotten.

The attached example reproduces the problem; move and resize the dialog, then press the button. I would expect the dialog to briefly disappear, then reappear with the same size in the same place but that's not what happens.