To reproduce, throw any potion and use this command while it's flying:

/entitydata @e[type=potion] {Potion:{tag:{Potion:"minecraft:healing"}}}

I was using command blocks to change the kinds of potions thrown by witches. I made them throw healing potions, instead of harming. I used the /entitydata command on a loop to do this. Here's the exact command:

/execute @e[type=Witch] ~ ~ ~ /entitydata @e[type=potion,c=1,r=1] {Potion:{tag:{Potion:"minecraft:healing"}}}

It seemed to be working just perfectly, up until I tried throwing potions at the witch. When I threw a potion at the witch, of course, it turned into a healing potion before it hit, but it also changed the potion I was holding. I threw a potion of harming. When it got near the witch, it turned into a potion of healing in my inventory. Could you please fix this? I want to be able to use /entitydata on potions without it changing the selected potion of the player. And by the way, I was on creative mode during all this.

More info: https://www.reddit.com/r/Minecraft/comments/3rmub5/15w45a_thrownpotion_entities_will_render_the_item/cwplbo0