Figured i'd post this here so that people know (as well as a friendly poke to the devs :P )

Some recipes require an item as well as materials. This item must be bought or found; if the item was created by crafting, it will not be accepted as an ingredient for the recipe. It will simply not appear in the slot.

This is clearly a bug because some recipes need crafted items as ingredients, e.g. Firotech Mk II.

For now, if you really want to craft something, make sure you buy the item ingredient to save yourself the rage at the alchemy machine later :P