Created attachment 108434 [details]
Screenshots

Font rendering is broken on specific widgets in specific styles after my system is upgraded to KDE Frameworks 5.37.0 using Qt 5.9.1, on NixOS 17.09.1502.19879836d1. The other relevant packages are fontconfig 2.12.1 and freetype 2.7.1.

With the font setting in figure-1, widget style set to `MS Windows 9x`, there are several mis-rendering cases. Figure-2 shows that bold italic face is only rendered correctly on title bar in Plastik. Figure-3 shows that italic face is mis-rendered on normal widget. Figure-4 shows that bold face is mis-rendered.

If the General face is set to bold, as in figure-5, it can be seen in figure-6 that normal text is rendered bold as expected, but bold italic text is still mis-rendered. For title bar, Plastik is still the only style in which bolt italic face is rendered correctly, as seen in figure 7.

This issue was previously discussed on the mailing lists. The links are https://marc.info/?l=kde&m=150728730630509&w=2 and https://mail.kde.org/pipermail/plasma-devel/2017-October/075248.html Another possibly related issue was discussed in https://marc.info/?l=kde&m=150828171918536&w=2