He writes: "I have a Zones 2-4 Oyster card, and travelled from East Putney to Swiss Cottage via Earls Court and Baker Street for a conference. Thinking it would charge me on PrePay for going through Zone 1, I decided to top it up, but when I got to Swiss Cottage, I was amazed to find it didn't. It was free. Gratis!"
"I've racked my brains about this, and I think that the Oyster system must have assumed that rather than taking the District line to Edgware Road, transferring for one stop to Baker Street, and then the Jubilee to Swiss Cottage (the normal person's way) it must have decided that instead I got off at West Brompton, took a Silverlink train to Willesden Junction, then took another Silverlink train to West Hampstead, walked about 300yds to the Jubilee line station, and took the tube south to Swiss Cottage. This way is obviously retarded, but doesn't involve going through Zone 1."
"So I think that there must be some code in the Oyster system that decides to be as kind as possible to you when pricing your journey on Pre Pay; even if that journey is utterly stupid. Is this something you've had experience of?"