I guess I worked around the "problem" already, but I'd like to report on it anyway, in case someone else looks for it.
Simply running the bitcoin binary spits out this error:
Debug: ../src/gtk/settings.cpp(276): assert "font.IsOk() && wxFontEnumerator::IsValidFacename(font.GetFaceName())" failed in GetFont()
I tried to ignore it by simply clicking "continue" but that does not work. Turns out you also have to uncheck the box that says something like "show this message again".
BTW thus far two other hits in Google with this error, one by a Ubuntu user who claimed to have solved the problem by changing the font in settings/appearance, but I don't have such an option under settings.
Neither does there seem to be a "gtk/settings.cpp" in the src/ directory of the program.
$ strace bitcoin
and view system calls.
I guess that the program tries to open a font file, not found this file and opens a similar font.