Did you consume it after initiating combat by pressing ENTER? Because I didn't see your character having the in-combat status effect.
I didn't manually initiate combat and then use it no, I'd started combat with the Lunatics and had ran back in that shop to reapply buffs and lure them through my gas and fire cheese
I hadn't checked to see if combat being "over" IE all enemies that could see you during combat were dead and being able to exit combat as soon as you end turn would allow you to use things that couldn't normally be used in combat, will remember to do so
To be honest I wasn't really sure if this was a bug or some kind of interaction I didn't realize was happening but I figured better safe than sorry and Styg can just call me a zoner to himself when he reads this