[da-anda]

However, when being in the movie section my memory gets filled until there is nothing left and the app crashes.

I don't know if it could have anything to do with the fact that I have a lot of movies, and the system tries to save all the fanarts and covers in the memory (just a thought).

I have a log for you here:
http://xbmclogs.com/show.php?id=37483

I experienced the same on Windows, so this is not Android specific. In my case it was related to a .bin/.cue ISO file of a movie XBMC/ffmpeg coudln't read properly for meta/thumb extraction and thus loaded the full movie into RAM. Same seems to happen in your case with "/storage/sdcard0/usb_drive_1/Filme/Alamo der Traum/alamo-a.bin"