Bold fonts not hinted correctly

Since upgrade to Ubuntu Artful, delivered with libfreetype 2.8.0, numerous hinting problems raised their head, most of which were solved upgrading libfreetype to 2.8.1. Hinting of bold fonts by libqt5 is still wrong though.

The attached picture shows the problem completely. Normal fonts are hinted correctly everywhere. The window title is Ubuntu 9 bold and somehow correctly hinted, while the bold headers are not correctly hinted.

libqt4 based apps are not affected as far as I can tell.