It is a dedicated server, but not one of my own. I am just a moderator on that so will see about getting you that other information from them. Until then though.,
1: It is effecting a handful of players at the moment, all those who have crafted the ammo thus far has experienced it.
2: It seems to only happen when you hit a zombie who is sleeping while you are sneaking.
3: No, I am not as far along as other players and they are pretty maxed out on perks/books whereas I am not, but I can replicate it on my end.
4: It does not seem to happen if the zombie is one hit killed. Only if they are shot and the electricity field appears does it effect the player.
Sorry for late reply, had a busy day