This game checks your Crafting skill when you try to craft something, and there are some recipes that have the same ingredient but give different results depending on your Crafting skill. Healing potions is one of them.
If you can't combine two Minor Healing Potions, it means your Crafting skill is too low.
PS: Crafting does work in stacks.
Last edited by Keizai; 15/08/14 02:22 PM.