Greetings.
First of all, allow me to briefly compliment you on a game well done in regards to capturing the spirit of old school computer RPGs.
About the bug :
Normally, you cannot put a Reactant in a Reagent slot and vice versa.
However, if there is already a Reagent in the Reagent slot, and you have a Reactant selected, you can swap places between the two, which results in a Reactant ending in a Reagent slot.
Vice versa works as well.
A very minor bug, and it practically doesn't affect gameplay at all. Just thought I'd point it out. I just hope I was clear enough. Don't hesitate to ask me to clarify if needed.
Keep up the good job,
- Idralmir.