My apologies for the delay, I was out of the office for holidays. I believe I reproduced your issue - not sure if they’re the exact steps you took but the result appears to be the same. I would expect that disabling Rewards would also disable Auto-Contribute and prevent the contribution from happening. I logged the below issue for this:
Thank you very much for reporting this issue and all the information you provided, it was very helpful!
I have not reproduced your issue yet (Rewards on, Auto-Contribute off with an empty table and contribution still occurs). I am wondering, since you said your balance went down, is it possible there was a UGP grant (the free BAT), you had in your wallet which expired? Those generally do need to be used within 30 days or they go away. This would cause your wallet balance to go down.
I’ll keep trying to reproduce in the mean time though. Let me know if it’s possible your balance change was caused by an expiring grant or if you have any other information I could use to try and reproduce. Thanks!