I’ve read this few a few times and I can’t see for what exactly you (think you) are being overcharged. You don’t say that you are being charged for WNP to HRY over and above what you have already paid to get to FOG; is that what’s happening?
You seem to be suggesting that as the default fare excludes zone 1 you should not be paying for zone 1, but as you *are* travelling through zone 1, the fare is payable.
You are correct in all your assumptions. The back office software will not adjust fares for a discounted Oyster card. On the return journey you should be charged as per the fare finder because the zone 1 bit hasn’t happened when you touch out at Wanstead Park.
Colin: I suspect that this fare will be changed once TfL have spotted it. The default will then assume travel via zone 1 with a cheaper option if you change at Shepherd’s Bush. For now it’s possible to take advantage of the anomaly by understanding how the system works.