It's the pointer, sorry for not specifying. Motion controls are relatively good, but not as good as before. The real problem is the pointer though.
I can't think of any light interfering, but I'll check that out next time.
Thanks for all ideas, I'm checking for blue-tooth now.
http://www.vgchartz.com/games/userreviewdisp.php?id=261
That is VGChartz LONGEST review. And it's NOT Cute Kitten DS