Not sure if this is a bug or what, but i noticed today on Hala that no potions are auto stacking, be it when you buy them or pick them up off dead orcs or whatever.
The still stack if you drag them one to each other but only after they are both in your inventory. In other words you cant drag it from the store/remains onto a preexsisting stack.
its not a biggie unless you have a full inventory, but it is a little tedious to sit there and buy a a potion, stack it with another, buy another potion, stack it with the rest, buy another, etc etc