I had an e-mail from TFL yesterday. Here's a section from it, verbatim, although I've marked the odd bits in bold.
You have successfully uploaded Auto top-up from <PickupStationName> station on your Oyster card, number <OysterCardNumber> and topped up your pay as you go. Auto top-up is now active on your card.<br><br>Whenever you travel on the Tube, DLR, Tram or Bus GBP<AutoloadTopupAmount> will automatically be added to your Oyster card at any station, using your credit or debit card ending in <HashedCCNumber>, when you enter a station and your pay as you go balance is below GBP5.00. You can change your Auto top-up arrangements at www.tfl.gov.uk/oyster.
Not the best correspondence I've had from online government. I've sent it back to their help desk in case they don't know they have this problem. But surely an obvious thing to see in any testing they carried out?