I am not English speaking, so I apologize in advance for possible mistakes.
Selected items in the panel "items that deactivate this potion" do not affect the potion in the game.
if you remove the bucket of milk, it will still have an effect of deactivaton.
if you want add another item to remove the effect of the potion, it will not work either.
mod for 1.14.4
Issue comments
I can confirm this parameter is set in the code but does not actually control if the item can cure this potion by the design of Forge and MC code.
I will remove this field as it seems that this field no longer serves its purpose and I did not find a good solution to overcome this limit in the code.
Attach your MCreator workspace (or even better a minimal example workspace required to reproduce the bug) please