When using Mac default style and a button that has too big font size, the button mac style is lost and it becomes plain grey rectangle, please find the attached example app to demonstrate this.

In the example, a chinese characters are used and when lowering the font size to 10, it fixes the problem. The same behavior can be seen with the other buttons as well if you increase the font size from 13 to 15

I think the problem here is that Qt tries to fit the text in the button at the cost of styling, but I am not sure if that is wanted behavior