[Andrés]

I had the same problem Last year (or a similar one).
It has nothing to do with filetypes, all icons change randomly but files are named correctly and opened with the correct program. It only appears after working for a while, using icons from programs you have used and dissapears after rebooting.
It seems to be somekind of mixup in memory.
Unfortunately I don't know what's the cause or how to solve it. It only dissapeared after I reinstalled windows (into a new clean folder) and then of course had to reinstal all drivers programs.