I noticed this too, and I figure it was an oversight in the development which we will have to live with for a long time. There were other potions like this previously that had similar problems....think most of them finally got fixed but we are talking about 2 years of living with the problem.
Kegs have their place, but they are not for me.
I use commodity deeds and stacks of bottles.
The trade off...
Kegs are cheaper than bottles....bottles should start at 5 gold per and if you are smart you can buy them at this price. But bottles can range up there pretty quickly if you are not a smart shopper. Player made kegs run about 250 gold for the smart shopper.
Kegs work better with the gardening program, bottles can be a bit buggy sometimes with it.
Commodity deeds allow me to put counts of 500 potions on sale on my vendor for those large bulk orders. This way my customers don't have to recall in with a beetle, buy 16 full kegs, recall out, bank, recall in, buy 16 more kegs.
Stacks of bottles take up 1 item count in your bank or house up to 60000 worth. To get that many potions in kegs you would have to take up 600 item counts. So bottles are better to stock up once and be done with it.