Noticed the problem with using run/ for transferring data to sdcard the hard way, tried moving my music to it via mtp (symlinked run/user/10000/media/sdcard so it showed up in mtp-mode). The transfer got stuck and I cancelled it. It stuck completely after that. Now the device complains that the memory is full -even after reboot- and there's nothing in my sd-card.

NEVER USE run/user/10000/media/sdcard TO TRANSFER DATA TO YOUR MICROSD.

PS: It was a lot of music.

EDIT: The problem isn't related to topic at hand