minecraft:potion cannot be placed back into creative inventory when clicking on a different minecraft:potion with a different name and effect. Same goes for minecraft:splash_potion.
MC-84331
Potions not being able to place back into the creative inventory
Resolved
Duplicate
0
You are getting MC-82986; it is trying to add to the stack (but potions can only stack up to one, causing the behavior that you are getting).