I experience some weird rendering issue with Roboto font (some others too), when Setting Enabled with Hint=Full and RGBA=RGB.
While most of Plasma DEsktop displays the font smoothly and without hiccups (dolphin etc.), some parts, especially the System Settings Overview itself behave strange, like having some mouse-over effect at work, which renders the font different as can be seen here:

http://www.netrunnerlinux.com/files/font-jumping.ogv

Most noticably is probably the "s" changing size...
I use Roboto font from here:
https://launchpad.net/ubuntu/+source/fo ... -1_all.deb
Most visibly it gets with the "Light" font-weight, whereas Regular also has the effect, albeit much less irritating.

Anyone have an idea what might be causing this and if there is a setting somehwere that could make the font display without that itch?

Seems bug in Qt's raster font rasterizer (in combination with the animated hovering implemented in some itemviews)

Try "systemsettings --graphicssystem native" - should be gone then.