This isn't really a bug but just something I'm waiting for you guys to fix and not sure if you're aware of it and if you're working on it right now.
The PoisonDartTower's(PDT) Poison Damage originally increased overtime on afflicted targets but that was removed in favor of just leaving the Poison Damage at a flat amount and with increased damage. On the release of the Journey Begins Patch someone probably turned on the damage increasing and forgot to turn it off. It wasn't mentioned in the patch notes and not alot of people seem to realize that its there or why its doing double damage.
(TL:DR) Every Poison Tick after the first is dealing twice the damage of the Poison Damage listed in the PDT's Stat.