Reply to Hitting play on 3 deck simultaneously?

I have a play button mapped for each of the 4 decks in traktor. Only thing is though I can only seem to play 2 at the same time. Say I have one deck playing and the remaining 3 cue'd up ready to go, when I hit play on the 3 buttons only 2 of the decks play and I have to hit the 3rd one separately. I'm using an external QWERTY keyboard to trigger everything and so now I've got a sneaky feeling someone is going to tell me it will only read 2 buttons when pressed together. Like a 2 key polyphony as such. Is this the case? Will I be able to play 3 decks simultaneously if I have a midi controller as opposed to a QWERTY keyboard?

Thanks