I ran into this issue last night and is reproducable.
Step 1: Put a flare in your hot bar.
Step 2: Take out the flare and use it.
Step 3: Switch to another item (hatchet)
Step 4: Place a piece of cooked chicken in the same hot bar slot as the flare was.
Step 5: Attempt to eat the chicken (it won’t let you)
Step 6: Move the chicken to your inventory.
Your chicken is now a flare.