I don't get why people would do this ... don't the bank just put their account into a negative balance? I read about another case in australia where an ATM was

I don't get why people would do this ... don't the bank just put their account into a negative balance? I read about another case in australia where an ATM was issuing $50 notes in place of $20 notes so once word got out a ton of people turned up to withdraw $80 - it came out as 4 x $50s = $200 ... but they were also asked to pay it back to the bank... http://www.couriermail.com.au/news/commonwealth-bank-atm-dishes-out-50-notes-instead-of-20-notes/story-e6freon6-1225778181276 http://www.couriermail.com.au/news/commonwealth-bank-atm-dis...