When you add gunpowder to an extended potion, it turns into Uncraftable potion.
To reproduce:

1. Brew any non-throwable potion.
2. Extend it via clicking the cauldron.
3. Add the gunpowder in the brewing stand.
4. The potions turns into throwable uncraftable. Just lost a ghast tear like this.

The only mods used are Origins, Origins:Classes, Extra Origins and Pehkui.

Oops, I didn't read it correctly. Thanks for the report, will look into fixing this.

To add on to this, the same issue is present in other mods which allow you to manipulate potions further.
For example, Extra Alchemy's vials, when used on extended splash potions, will produce a vial with the name 'Uncraftable Potion', though it still works as intended.