On Dec 3, 10:32 am, wrote:
ISTR (but can't find confirmation) that if you enter a station with
your PAYG Oyster and leave it again (within a short space of time) the
journey is cancelled - ie no charge. To cover the case of you finding
the service disrupted and deciding to abandon your journey.

That's not my experience. On one occasion, I entered Moor Park
station, realised that I'd forgotten something in the shop. So I went
back out through the barriers (within a minute of entry), the original
£1 entry charge was not refunded and when I returned, five minutes
later, I was charged £1 again. The £1 was the expected fare for a
Saturday, as I had a zone 1-2 annual travelcard on the Oyster as well.
However, there was no problem with getting it refunded when I phoned
the Oyster helpline.