Since the Hornet headspaces on the rim, that headspace amounts to the amount of gap from breech/barrel face to reciever. In this case, there has to be too much barrel to receiver gap. When the round is fired, the case grips the chamber wall keeping it from moving back to the receiver and reseating the primer. When it was converted to K, it didn't have anything done to change that gap. When you barely kiss the shoulder when resizing, you are taking up some of that barrel to receiver gap, which is fine unless you get so much the action can't close.
Marv's solution is fine for the once fired brass.