A thought came to me a while ago; With the
Machine Doubling happening on coins, there is no way it could be a hub issue. The devices are tapered from top (narrow) wider at the base. With the mark that MD makes in a device, there is no way that it would release if it was hubbed into the die that way. So it stands to reason this can only happen when the dies move/bounce during a strike damaging them with a horizontal movement. (Moving sideways) Even The bust and the central reverse designs are tapered top (narrow) wider at the bases. This is so the coin will release from the die.