BBC said:London bus contactless system charging wrong cards
One hang-over from introducing contactless bank cards on the buses to pay for your fare, is that some people are being charged on the wrong card.
This happens when your bank card and your Oyster card are next to each other in your wallet.
Transport for London (TfL) did warn passengers this could happen.
It could mean you could be charged twice for your fare, for example if you have a weekly travelcard loaded on your Oyster card and when getting on the bus you are charged on your bankcard.
I've also been contacted by TfL staff who are getting charged on their bank card instead of their free staff Oyster card.
Not high number
The numbers are not high at the moment, Tfl claim they have only been contacted 60 times so far about incorrect charging.
(Full Article)
It seems when presenting a wallet with both an Oyster (possibly containing a travelcard) and also a contactless bank card, sometimes the bus will charge the bank card if that's the only one it detects.