@Nanocore: it's probably jffs2_gc_mtd4 (jffs2 is built-in memory's filesystem type and gc is probably garbage collection) compressing the filesystem. nothing to do with kagu, could you check how much space you have left on by running "df -h" in an xterm and looking for the "mounted on: /" line? do you have maemoscrobbler installed/enabled, maybe it's the db file getting too big? check how big it is by running "ls -lh /home/user/.maemoscrobbler.db" in xterm (if it's a few megs and you're running out of space, just do a "rm /home/user/.maemoscrobbler.db" to delete it, it will be recreated next time you play a song.

@faye: could you install mplayer if you haven't, and change the default player to mplayer in the main menu? (the option should be available once you install mplayer) i suspect it's a nokia bug, kagu code is pretty straightforward and organized, and your symptoms don't fit the code at all.