We had a VF0 do this running unattended on a long cycle job. I came to the conclusion that the tool had moved in the carousel due to the vibration from a heavy cutting sequence that had the whole machine shaking. On a couple of occasions previously it had dropped a tool during the tool change and when I checked I found a few tools had moved forward in the fingers in the carousel. Needless to say all hell broke loose when the tool hit the job and jammed sideways in the spindle running at 7500rpm. We could see that it had been gripped with balls in the gripper riding on the rim of the pull stud not down on the angled faced and we could see the grooves they made as the tool was pushed sideways. The spindle taper was damaged so we took the machine off regular production and just use it for rough work now. But in two years since then it has never missed another tool change and it has done thousands.
An open mind is a virtue...so long as all the common sense has not leaked out.