Collecting train tickets bought on line at the station

http://stibasa.blogspot.co.uk/2015/01/collecting-onlne-train-tickets-at.html

I went to Barking station today to collect tickets that I'd bought on line. I went to use one of the larger, older ticket machines (non Oyster) and noticed that it asked for a payment card to be put in. I put in one of my cards, but not the one I paid with. There was no problem with that, but I couldn't complete the transaction owing to a fault with the on screen keyboard.

I went to use one of the newer ticket machines. The display said to put in the card that I'd paid for the tickets with, but I used another one (as above) and still got the tickets.

Obviously both the cards in question are mine, but the one I used has not been in a ticket machine before, and has not been used to buy a train ticket. Therefore I have reason to believe that any valid payment card would work.

The tickets were for Euston - Rugby.