One thing that occurred to me is you can come at it from the other direction: a glitch causes both copies to survive, in which case you would essentially have proof it is a copying process, not a translation of an object from one place to another. And you'd also have a bunch of interesting legal problems to deal with.
This happened at least twice. Once in TOS (S01E04), where Kirk was covered with an ore and it caused two Kirks to come out of the transporter, one good and one bad. And it also happened in TNG (S06E24) with Riker. There was a second Riker living on a planet for 8 years because of a transporter malfunction. Riker 2 ended up being a semi reoccurring character...I remember him coming back at least once in another episode. I think he became an adventurer/pirate or something.
