I don't think in this specific case it does, though. I had similar problems with a completely different distribution. I'm convinced that it's an upstream Qt or KDE issue where broken caches or changed cache formats don't get automatically invalidated and rebuild. In the case I vividly remember some lower level graphics library was updated and everything seemed to run fine but for some (and only some) users it resulted in Qt or some KDE component not being able to parse the cache any longer. After some research (under Gnome) I wrote a small script that quit Plasma and KWin, deleted all the caches (icon, font, ...) and then launched KWin and Plasma again. Worked fine and came handy on a couple of further occasions.