Reply to Mapping suddenly changes during DJ set !!!!!

I am using Traktor Pro 1.2.7 with an NI Audio 2 soundcard and a Vestax VCI-100 Controller on MAC OSX Snow Leopard 10.6.8. This worked flawlessly for awhile. Suddenly this week, all the controls will all start doing different things than they should in the middle of a DJ set (IE. My knob assigned to FILTER will start controlling KEY instead). This will happen several times during a set, sometimes within minutes, and then I have to reload the mapping while playing to get everything to snap back to normal. This happens on a fresh reboot with nothing else running in the background. Does anyone know how I can fix this?