Reply to Pitch Control / Sync Issue

Im sure the answer to this question is going to be something dead obvious but i cannot work out what i have done to cause the problem below. I was DJing in Manchester last evening , during my set at random intervals (ie: when it chose to) my Traktor 3 software started trying to sync to the BPM of the opposite deck (the one on pause). In other words while the track was playing it started either moving up (+) or down (-) with no help from me. I have tried to replicate the issue this morning but have failed, but am worried it will happen again just as the dancefloor is rocking. What button have i accidentally pushed ??? Any ideas would be appreciated. I am using the Vestax VCI 100SE.