It's the MOLD. We get this a lot on the ship. Prepared Pancake mizes that come in a box as opposed to a sealed polybag can grow mold. The usually culprit is often listed as Aunt Jemima's. The reaction is to the mold or the waste product from the mold and not from any "chemicals" in the mix. The mixes were fine to begin with but get contamined with mold spores once opened or stored in somebody's house or some pirates galley cupboard.

Moral of the story - toss all bakery mixes more than 6 months old or at least buy the kind in the poly bags and then once opened - toss if not used up after 6 months from date of purchase