Hit Monkey Purifying All Debuffs

Mofugger

Fighting Hit Monkey on Path B in 3.1 of this month's quest. Using Dr. Voodoo. Hit Monkey has a bunch of physical resistance buffs when I launch an SP1, let's say 10, and 5 Loa buffs. Based on Hit Monkey's description for Primal Rage:

Gain a 100% chance to Purify one of each Stun and Damage over Time Debuff on Hit-Monkey when one is gained, or when Primal Rage activates. Purifying removes Primal Rage.

I expects that he will get 15 Spirit Venom debuffs, and then purify 1 leaving 14. What actually happens is that he purifies all Spirit Venom debuffs. I'm not sure if it's a gameplay bug or a documentation bug, but those things don't match.