QPushButton's bounding rect seems to exceed the button itself by so much that you can click the button by pressing clearly outside of it.

This can be reproduced using the Extension Dialog example that ships with Qt.

Click on the "More" button, but do not release the mouse....
now move the mouse up and down... when the button goes back to grey, you are off the hotspot.

This causes trouble when having multiple buttons stacked vertically for instance. Customers keep clicking the wrong button because they are close to each other.