I'm not sure, but I'll share with you a tip that my BF gave me (he teaches Kung Fu, so it turns out, I'm actually doing Pole Fu! LOL).
He suggested, once you get into your handstand, that you rock back and forth from side to side just a little. Not enough to throw off your balance so you crash to the floor, but just enough to find your center. You soon learn how forgiving your handstand is and your body tells you what to tighten or relax in order to stay inverted.
If it's a strength issue, then one thing I do to condition for handstands: Start in your basic invert. Slide down to your handstand. Walk your hands out about one foot from the pole. Bring your chest down to just a couple inches above your hands. Push up and back like you're doing a caterpillar climb. It's basically an inverted push up, using your feet to hang on to the pole. Do about five or ten of those and then go work on your handstand against the wall. Worlds of difference.