ZDoom

Load attached file and start new game.
After spawning type into console "summon dio". It summon dummy player pawn.
Press use on it and you change player from "default" player pawn to newly spawned.

After this press crouch button. Both player pawns change sprite/state from "stand" to "crouch".

I can confirm this happens even with just vanilla voodoo dolls. Crouching propagates the sprite change to all of them.

Perhaps a small change to P_CheckPlayerSprite could be done so crouchsprite setting doesn't affect voodoo dolls?

Correct.