Witches are not affected by potions or Potion affects. I saw an issue already created with this bug in it, but it was a duplicate and with multiple bugs reported in it. Also, this may be working as intended, because I did not do much research beforehand!
Witches do act as if they are angered by it, though, because if one hits another with a thrown Potion, the other starts "fighting" with it (i.e. both staring at the other and throwing Potions at it).
Steps to reproduce:
1). Spam a Witch Spawn Egg in Creative.
2). Change to Survival (Preferably with Diamond armour, if you want to survive long enough to see the bug!)
3). The Witches will start to fight one another, doing nothing.
Comments 4
Ah, thank you! Yes, I only just saw that and was coming back to say that (but my computer and internet is slow I only just made it!). Maybe I should look before I leap. My apologies.
Whoops, accidentally re-opened the issue thinking it was about something else. (Misread "potion" as "poison".) :S Re-resolving...
This feature works as intended.
Witches are immune to some effects, like poison, and potions of harming are greatly reduced against them. However, they still view it as hostility. Please visit Minecraft Wiki: Witch for more info on the witch.