Created attachment 103814 [details] this is how it look. There are different font rendering between left pane and right pane. The right one was better. Sorry if my words couldn't describe what the bug is, but please look at the attachment.
Created attachment 103815 [details] also this
Some information that might be useful. It was a fresh install from openSUSE Tumbleweed. Fontconfig version is 2.7 but I set the interpreter to version 35. Changing back to 40 not helped at all. Anti aliasing is On, sub pixel rendering is RGB, hinting style is full.
The difference between left and right part is that the left one is written in QML, while the other is still QWidget based. I guess QML uses different font rendering method/technique or whatever, which is something I really know nothing about and I'm not sure I can do anything about it. In my case both parts have same font rendering as I can tell.
Jan, It is possible to force native font rendering (i.e. same as in QWidgets) in QtQuick based texts. See http://blog.qt.io/blog/2012/08/08/native-looking-text-in-qml-2/ If this does not help, please ask on the plasma-devel mailing list.
Created attachment 103897 [details] Proposed patch Can you please try attached patch?
Ping? Nobody else has complained about this problem. Also looking again at your screenshot I don't see any difference in font rendering. The reason why left side looks different compared to the right side in your first screenshot is that apparently both your connections are connected and in that case bold font is used and the description below uses different color. I'm going to close this issue now as I don't see any problem.
The difference between the leftmost list and the rightmost settings page is obvious. I suggest to apply the patch; most (if not all) Plasma texts use native rendering.