A new way to screw up pistol ammo...big time!

While at the range last Saturday (April 2) I was shooting a recently acquired S&W 44 mag. with moderate handloads. I loaded six, shot them, loaded six more and shot three...then the gun wouldn't cycle (cylinder locked up). Thinking that I had a bullet backing out of the case, a common problem with light guns (28 oz.) and heavy bullets (255 gr.) I asked around for a range rod. After borrowing one from another shooter who was more prepared than I, I got ready to beat the bullet back into the case...
To my surprise, the obstruction moved easily (no hammer necessary) and I opened the cylinder and extracted the fired cases and the three unfired rounds. What should I behold...a 44 mag case with a 9mm case inside it! How did this happen???? Well that's the easy part. One of the 44 cases I loaded on my Dillon XL650 had a 9mm case inside it...the decapping pin went through the flash hole on the 9mm case, on down through the flash hole of the 44 case, having punched a hole in the 9mm primer, it removed the 44 primer per standard procedure, and after seating a new primer, powder was added and the bullet seated. When the firing pin struck, the fire went up through the flash hole of the 9mm case (remember the hole in the primer?) and lit the powder on fire, it did the usual and the gun fired normally, but in the process, the 9mm case moved forward just enough to lodge in the cylinder gap, locking up the gun....wow...who'd a thunk it?

See photos...
#1 looking into both after separating them
#2 looking into the 44 case before removing the 9mm case...note rolled edge of 9mm
#3 side view of both cases....note undamaged 44 case and bulged 9mm