C15-S to iPad and Mac

[rih]

Hi, I have problem with playing Korg C-15S through midi to iPad or Mac.
I use Garage Band and with connection between iPad or Mac is everything ok, but as soon as I try to play polyfonic, one of the tones I play goes to loop or how should I say...neverending sustain. I think there is something to do with 'note on note off' but I don't know what to do. I also try some free software just to be sure that the cause is not GB but effect is just the same. Also there is some strange tone (duplicated?) when I release key. It sounds like I'm playing both by pressing and depressing key. Without midi piano plays perfect. Please, any suggestions?