The effects are supposed to get corrupt effects if they have have a amplifier higher than 127. For example:
Use this command: "/give @p potion 1 820 {CustomPotionEffects:[

]}"
It works fine. You should get a corrupt potion of health boost, and it works as it should. (You lose hearts)
Now, if you use the /effect command to do that, it won't work.
Try using: "/effect @p 21 10 128"
This command should give the same effect as the potion, but instead, it ignores the fact that it has a amplifier higher than 127, and just amplifies the effect, instead of corruptiong it.