just to update anyone else who runs into this problem. First, Mike rules. Thanks so much for your help! Second, I had a pre-existing "pending" in the taxonomy table, so then WC couldn't use it and reset my orders appropriately. If all your other IPN stuff is working, go to the system status and check at the bottom to make sure your statuses all look right.
Thanks again to Mike, this was a very specific situation and I am so grateful Mike and Woo took the time to get me on track!