Witches continuously throw potions even when the player gets >10 blocks away where there is no way the witch could hit them.
This could be intentional, but seems unlikely.
As a result, they seem to be hitting themselves with their own splash potions a lot more than usual. (This in particular happens more on very uneven terrain)
Can reproduce. At a distance of 14 blocks, on flat terrain, the witch throws lots of potions but none hit.