If I see that one (or more) primer has gone into the primer magazine upside down I watch the primer slide as I'm loading so that I can fix it before it gets seated in a case. When I see the upside down primer in the primer cup I pull the case out of the shell plate and push the handle forward (on a 550). Then I just use a small piece of tape to lift the primer out of the cup, flip it over and drop it back in. Slip the case back into the shell plate, seat the primer and continue loading.
Tom