Just to clarify what the idiot (me) did... since my writing is isn't all that clear...
I forgot to feed the thing a shell, and didn't catch the mistake until cycling the press with a vacant second station. That station primes and drops powder.
The key point, and the learning experience here, is that if you do that the powder drop tube can pick up the primer that was waiting there to be seated in the shell you forgot feed it. It's out of sight in the tube, jammed there by the powder that was dumped and it could very well make it into your next load.
