Can Not Reset to Default Style

Under older Qt it used to be possible if you changed the style that you could reset to the default style when the application started by setting an empty stylesheet. This does not appear to work anymore as the following Stack Overflow post no longer works in the latest Qt:
https://stackoverflow.com/a/7717996

Use case is a preferences dialog that allows the user to choose one of the styles from the style factory keys. The user can choose a style and apply it. They can also "Restore Defaults" to have their QSettings cleared, at which point the style should be reset to what it was when the application started. When this happens, there's no way to tell the QApplication to reset its style.

I consider this to be a regression as the SO topic suggests a solution that used to be a way of achieving this use case, but it no longer works.