When i was in HS, this restaurant in town opened a new arcade room, which had some of those machines. I eventually found out it could take pennies, so I used like the ten or so I had and got a few tickets. Then I planned a scheme to go to the bank, get a roll of pennies, and win big time. Well, by the time I came back like a week later, they fixed the machine and it no longer took pennies :( must have saw the pennies I put in and freaked out.
I did a google image search to try and see if there was any information and apparently this is just a thing that happens, as there are many pictures of piss bags like this. From what I can gather, it's always the low urinal this happens to when there's an obstruction that causes the other urinals to backflow into the low one.
Although I'm sure there are always assholes who will actually pee in the bag.