When I first started reloading I worked everything in batches. I deprimed and resized a huge bucket of .45 ACP and then stored them. I'm still using some now and then from that bucket a couple of years later and not a single one has ever had this phenomenon happen to it where it springs back out again. I would hazard you must have either used a universal decapper die or otherwise popped out the primer and not resized them. I was going to say you could check the bullets to see if they are in spec but that would ignore the missing primer.