If you use the command: /give @p minecraft:potion 25 16389 the nearest player is not given a stack of 25 healing potions, but 25 unstacked healing potions. I don't remember seeing this being a change in this snapshot but if it is, it's going to break many "redstone driven" maps out there.
MC-65753
/give splash potions do not stack
Resolved
Duplicate
0
Looks like MC-3444 was fixed