This is a HUGE bug considering that poisoner is the Neutral Killer in most modern Mafia games.
My save had all options for Poisoners off. This means no notifs of poison, poisoned people die 1 night later, and Poison should NOT be cured by Doctors. That last part is important.
Now, from the POV of the Poisoner: 4, here's who he poisoned by day.
N1: Poison 15
N2: Poison 12. 15 dies to poison.
N3: Poison 3. 12 dies to poison.
N4: Poison 1. 3 DOES NOT DIE TO POISON.
Game ends on Day 5 with Poisoner being lynched by 1 and 3.
1 was a Doc, so let's see what he (or rather, I) did.
N1: Heal 12. 12 not targeted by poisoner yet.
N2: Heal 15. "Your target was attacked!", 15 dies to poison.
N3: Heal 3. "You have cured your target of poison!" "Your target was attacked tonight!"
N4: Heal 3 again. "You have cured your target of poison!"
So it appears that 15 couldn't be cured, but 3 was somehow? 3, the Town Constable with the LARPy Nazi Name, is causing glitches on his end, so lets analyze his actions.
N3: Attacked by triad, healed by 1 the Doc. Given a vest.
N4: Puts on the vest. Nothing else happens.
Ok so now lets compare what happened in the last 3 nights.
Night 2: The doc heals 15, who was poisoned. 15 dies to poison anyways.
Night 3: The doc heals 3, who was attacked by triad. The doc is told that 3 is "cured".
Night 4: 3 vests, therefore stopping his poison-induced death. The doc is told that 3 is "cured".
Vests prevent your death from poisoner. Any feedback regarding vests triggers the "cure" feedback for doctors whenever targetting those with vests who are targetted by poisoner.
This goes against the very idea of Poisoner being able to go through night immunity. The Godfather isn't safe, but a dude with a bulletproof vest is? Vests can't prevent poison irl. Please fix this.