Whenever you give yourself a levitation effect, it affects potions you throw.
In the video that I added below, you can see me giving myself levitation with a 255 strength, this will cause me to maintain my altitude. (1-127 will go up, 128-254 will go down, 255 will keep the same altitude)

However, this will send any potion I throw straight to heaven. This does not happen when I have no levitation effect. This happens with any type of potion I throw and with projectiles like snowballs or eggs.