We have had IB switch itself on in the past. Also, our cancellation policy moved itself from Flexible to Moderate, which complicated this situation because the guest couldn't cancel on her own.
But no, IB was not on this time. It's happened before, where it says one of us accepted the reservation when we did not. This time, we were together and neither of us had our phones out for an hour or more on either side of that "acceptance time". Very frustrating. After 5 calls to support and the help of a fantastic guest, we managed to get it canceled without penalty.
Thanks for your reply @Mike-And-Jane0.