There is no answer to this question. If your core feels unstable during any exercise, then add some core work and/or focus on it during the exercise until you do it right...
Derek- get some sleep!
S. Emile Hughes
Current Lifts (December 2010): BW 166lbs; 285lb Bench Press; 315lb Squat; 175lb Overhead Press; 405lb Deadlift; 205lb Power Clean