I just took my puppy to the animal hospital tonight. While there, a puppy came in and tinkled on the floor. The vet said it is something that puppies do to show submission. She said her boys would invite their friends over to her house to watch her one year old puppy piddle. Only this puppy rolled over on her back and piddled on herself! The boys thought it was the biggest joke but the vet said, "Hey, this isn't a side show!" and made them stop.
I noticed there was always a roll of paper towels and spray disinfectant handy.
Not much help, but maybe a little more light on the subject?