System styles such as those from Windows and macOS ignore certain hints and draw controls as expected for these platforms. Qt follows the platform user interface guidelines closely to ensure that applications looks as expected.
Any reason why you didn't use, say, static QPushButton dummyButton; here?
I guess I fumbled to long to actually get the style sheet to apply. I tried many different things (because I didn't see this documented anywhere). Must have overlooked this when cleaning up. Thank you! Will fix it in my code.