Placing an awkward potion in the bottom slot and a pufferfish in the top results in a water bottle rather than a potion of water breathing.
The same happens trying to add redstone to a potion of fire resistance.
The cause might be that the strings are mismatched between obfuscated classes 'acd' and 'acf': "water_breathing" and "long_fire_refistance" versus "breathing_water" and "long_fire_resistance".
Linked issues
duplicates 1
Comments 2
Has been fixed in 15w31c, according to MC-84131.
Not a duplicate. This bug is about a recipe failing to work correctly, while that is about recipes that were just completely removed.