Stopping clips

Hi, I'm an MPC Live 2 newbie and have noticed that if a clip is playing and I have an external keyboard attached, when I hit a 'C' in any octave it stops the clip. I can't seem to find anything through search on here or the internet (or manual) any quick explanations? Also without the note stopping the clip I actually can't find a way of stopping it if I have it in loop mode or one shot so bit bemused

Sorry if I'm being dumb!

STeve