I've been teaching this for years and have done it myself in rough conditions without ever breaking a paddle shaft. My 1st guess, sight unseen, is that you're climbing on the paddle. there is no point in this maneuver that you should have all of your weight on the shaft of the paddle, it goes on the deck of the kayak.
I also discourage the systems that attach it to your boat, this almost guarantees ripping hardware out of it. Hold the paddle to the coaming with the hand that is closest to your coaming when you are aft, with the paddle shaft between yo u and the coaming