I actually went to a stamp vending machine yesterday after I read the news. I know the machine will return the changes with $1 coins. I bought 20 stamps with a 20$ bill and it returned 12 $1 coins, of which some of them were gold colored that supposedly have a chance of missing 'GOD'.
I went back to my office and found none. I began to think the guy put the changes in must have thoroughly inspected every $1 coin.