Modified NBT potion has effects modified by game - NBT Potions do not work, In the screenshot, you will notice a modified NBT potion tag on the potion, however, a jump boost effect given by the game to the potion cancels out my effect.

1. Modify any potion with NBTEdit using CustomPotionEffects tag
2. when editing is complete, save what you did in the NBTedit, then go back into game
3. Look at potion, your customized potion has turned into one of the game's default potions (Speed II, Instant Health II, etc...)
4. Look upset :'(