quiz button text

I've noticed a really strange thing on the master slide for Quiz questions. There doesn't seem to be a way to adjust the position of the text on the buttons. When I click on the "Submit" button, I can change the kind of button, the color, the text color, the font, the size of the button, but I am not seeing where I can set "SUBMIT" text to be in the center of the button. Perhaps not a big deal to some folks, but the text sort of defaulting to be left justified just doesn't look as polished as text that you center both horizontally and vertically. Is there a global setting somewhere by chance?