This has happened several times over the years and it always takes me a while to figure out why my checkbook balance is suddenly off, and then I remember the opening balance issue. That balance is deleted by Quicken so altering your current balance.
The thing I was doing today was deleting transactions in another bank check register that had inadvertently been placed there when editing a reminder transaction that I was trying to enter into my register. I only mention this is case it helps someone isolate a cause; of course it could have been something else!
I'm not the only one to see this. See: