This is most definitely a Qt 5 bug, there are dozens of these, most of them I have managed to workaround, a few, like this one, I cannot. I suggest you use the fonts that work and wait until Qt gets around to fixing this issue.
Text rendering in Qt is a real crapshoot, there are many text rendering bugs that Qt 5 fixed over Qt 4, and some that it introduced.
EDIT: see
https://bugreports.qt-project.org/browse/QTBUG-40912