My son stumbled across a little known oddity of making a same station exit last month. He touched in at Crayford and after a few minutes was informed that the line was closed because of a fault. He touched out and I drove him to nearby Slade Green where he touched in on the validators. Further along the line his card was inspected by a Southeastern RPI and he was told it wasn’t validated. Thankfully the RPI responded to my son’s protestations by scrolling back through the journey history and he noticed the Crayford to Slade Green journey. He decided to let my son carry on, and on touch out at London Bridge an incomplete journey was recorded. I called TfL the next day and they refunded the overcharge.
What actually happened was a mystery to the customer service staff at TfL,