First noticed during a mirror duel vs
ddevans96, this bug was confirmed during a second duel.
What appears to happen is that hatching an Egg produced by a MitoSoR'd Egg would produce a random creature (usual behavior) plus a copy of that creature (which looked as if Parallel Universe was casted on it.
This copy ("ghost") would vanish at the end of the turn, deal no damage, fail to mimic actions of the original creature, and generally leave no trace of its existence. This makes me believe that it is merely a graphical error, but I have not tested it extensively.
We confirmed through the ingame chat, and afterwards, that we were indeed playing each other (as opposed to an AI) during the match.
Things I have not tested: Hatching Eggs that did not originate from Mitosis after the combo is played; behavior with a full field (therefore no place for the copy to appear)
We also desynced during the second match (though not the first) and this behavior was consistent throughout, which is to say that it was not caused by desync.