QPushButton checked state stylesheet does not apply font styles

When I define a style sheet that modifies the font style in checked state (but also in other states) it does not display the text in the selected style.
I have defined a style that tries to draw the text in bold when the button is in checked state.
QPushButton:checked

I have tried various style sheets e.g. font: bold or font: 30px
Setting the color to some other value works, e.g. color: red

Attached an example application that shows the problem. When clicking on the checkable button, the text becomes red, but not bold.
Setting another button to bold works, just not in the checked state.