In the Origins add-on Classes one of the selections is a 'cleric' who has the ability to make brewed potions 'extended' (doubling the potion's duration) using a cauldon. The potion bag doesn't accept these potions as legitimate items to be selected, although they can be stored in the storage area of the bag.

Thank you for your time.

The Origin: Classes mod uses an unorthodox method to lengthen the potions, which is done by including the effects in a custom potion tag. The bag can't recognize what potion a bottle contains, so it won't use them. I'll investigate if there's a way to determine which potion to use in a simple manner, but I make no promises