I've had that happen a few times on my Quadra 52. Running it into the high grass always resulted in instant retracts and a broken prop. Now I safety wire the bolts if possible or the entire muffler.

rclooney, a gas engine carb is a little different than glow but this can happen with both. Once the muffler comes off it changes the back pressure and usually the mixture goes lean and RPMs go up. Gas engines are not always stopped by cloosing the carb all the way in this state.