In the snapshot 13w09c, throwing a splash potion of harming (Instant damage 1 or 2) doesn't affect you at all.
It's easy to reproduce, just start playing on 13w09c and try it yourself.
Comments 5
Works fine for me. Having armor with the Protection IV enchantment prevents most of the damage from the level II potion and all of the damage from the level I potion. Other factors include distance from the impact site and timing (ie. if the potion activates on the same tick as a regeneration effect occurs, such as from having a full food bar or a regen potion/golden apple/beacon effect active)
You are right, now it works for me again. I don't know what caused the problem in the first place, but when I tried again today on 13w10a, it was back to normal...
Works for me. Threw it right up, got hit and damaged by both types.
Make a new world and try it there to make sure it's not some world/rule setting.