Hi alekmaul,
Remember that bug with the function oamSetXYEx, if your set oamSetEx as OBJ_SMALL and value of X in oamSetXYEx as value negative the sprite is changed for OBJ_LARGE while this sprite is negative I quoted here http://www.portabledev.com/smf/index.php?topic=324.0
you can find any solution?
sorry, didn't remember that bug, will check the lib :/