Every once in a while (every couple of weeks), letters seem to get scrambled up in Ubuntu. What I mean is that some letters (sometimes more, sometimes less) get replaced by weird symbols. For example now it is the letter x that got replaced by a weird h-like symbol everywhere in Ubuntu that uses this default font, for example in GIMP:
What could be causing this? Sometimes a lot more letters get messed up. If I log out and log back in it's good again. I have no idea where to start solving this.
Edit: if I highlight (select) the text (for example in a search box) then the correct letter appears, although only if the number of selected characters is small. But when I unselect it again, it's bad again.
Edit2: Now another example came up:
This time it's only in LibreOffice Calc. Very strange.