Quote from the link below.
http://www.iworkforfgw.com/viewtopic.php?f=4&t=18&start=0&st=0&sk=t&sd=a"Another problem at Paddington is people blocking ticket machines, so people putting in notes in, if they get rejected notes cant come out. Customer goes ticket office. Thief goes to machine, unblocks and takes money. There was a person arrested and charged for this recently I heard, whether he same guy who does Paddington I'm not sure. Just be aware if you believe your money has been swallowed by the machine, check it hasn't been blocked."