Save a copy of the original return with a different name, and don't use that for amending. Just keep it so you have an unmodified copy in case TurboTax saves without asking.
(It does sometimes save without asking. I don't know exactly what makes it happen, but it does seem to happen at some point in the amending process. I agree that it shouldn't do that, but since you know that it does, you can protect yourself by saving an extra copy.)
I go back and try the Amend process again - bring up TurboTax again, checking the Amend Return option and then using the just saved file as input for the Amend process - and it still comes up saying that I am due a Tax Refund of $13,492
It doesn't reset the refund to zero immediately when you start to amend. Does it reset if you go a few steps further in the amend process - at least up to the screen that asks you what you need to change?
