This is a pure guess but it has happend to me.
part taking a cut chuck pressure was low to keep from distorting the piece and when the tool came in it knocked the peice slightly and then on retract it yanked it out of the chuck, the chuck then closes more because its still under pressure and the alarm chuck unclamped comes on.
its happend to me before. one other thing that I've had happen is the low pressure switch stopped responding and I spun the chuck up to 4k and not enough pressure to hold the peice and bang boom!
thanks
Michael T.
"If you don't stand for something, chances are, you'll fall for anything!"