I have one, use it a lot. I can't imagine how one could get stuck, but of course you are going to have to investigate that somehow. It would certainly not be easy to get one stuck.
I guess when you look at the lower bead breaker you can see objectively that it's down, right?
Over the years, anybody could have removed some of the airlines and cause it to behave differently, but that would be dumb. It would make more sense if something was broken and air was just blowing out with the pedal up or down.