I updated from 1.8.7 to the new 15w31a snapshot and realized that the fire resistance potion that I always keep in my inventory had turned into a Water Bottle. However, the icon displayed wasn't either the fire resistance potion's nor the water bottle's but a 4-squared black and purple one.

I went to see my potions chest and all potions were displayed as water bottle with the same bugged icon.

Water bottles did have their icon correctly displayed.