Dripping Dead stuck and unkillable inside completed event pillar

I completed some sort of event inside the Fetid Pools where you activate the center pillar, and monsters spawn out of 3 plants around it that you have to kill. There's a groaning zombie stuck inside that center pillar and he's also the last monster required to complete the quest "A Dirty Job".

bug report ref # 780620577

I have exactly the same issue. ! zombie is stuck in that pillar and i can't kill it with anything thus am unable to finish the quest.

do you know how to deal with it?

I'm having the same problem I can't kill it no matter what I do a zombie is stuck