(Valid as of ZDaemon 1.10.19)
In the original Doom, effects of voodoo dolls (additional Player start #1-4 things) were tied to their respective players (1-4). In client-server source ports with players coming and going while a map is being played, keeping this 1:1 mapping is not possible. The perfect solution does not exist, but ZDaemon tries to keep most WADs playable by using the following rules when it comes to voodoo doll behaviour.
Artifactunless one of:
*This may not be the intended behavior, and a change is being considered.
ZDaemon exhibits one peculiarity when it comes to scrollers which is relevant here since voodoo dolls are often used in combination with scrollers. The peculiarity has to do with scrollers moving extremely slow under certain conditions and its description can be found in this Doomworld post.