Comment # 11 on bug 1149986 from Xu Zhao

(In reply to Marcel Kuehlhorn from comment #8)
> Created attachment 818690 [details]
> cursive chat titles
> 
> I also noticed that in your patched version the titles in the chatlist
> become cursive, is that intentional?

Tonight I debugged it on a xfce virtual machine.
Some updates:
1. The libqt5-qtstyleplugins-platformtheme-gtk2 package has two so files:
platformthemes/libqgtk2.so and plugins/styles/libqgtk2style.so. The problematic
one is libqgtk2.so.
2. Qt plugin loader searches the folder /usr/lib64/qt5/plugins/platformthemes
and finds two plugins: libqgtk2.so and libqgtk3.so. It incorrectly selects the
libqgtk2.so even if it is a gtk3 environment (xfce/gnome in my case). If only
gtk2 plugin exists, it has no problem. So it is really a Qt bug.

Up to now it is not clear why Qt prefer the gtk2 plugin over the gtk3 one, and
whether a workaround exists.