[quote=Tachi]
I suppose it's less a rule and more "something that came up during conversation about how things work". Not sure if it was on the old RPG or another site Psy ran this on, but um, yeah.
[/quote]

It was on the original RPG I ran on Tropes. The reason I had it so that the shards don't do that is unrelated to the Sayaka subplot. I'm trying to think of why it's not applied in this RPG, and the most I'm thinking of is that the Shards work differently in JLM than in TOS, and thus there's no Orton Syndrome (a term to describe the Shard's personality taking over its host)