Kubota L 4600. Brake on, working in a creek for an hour or so. Finished my chore. Went to get on the tractor and, without touching it, I raised my leg to climb on the beast when I heard a click. Brake released on it own and rolled off into the creek exactly where I was working. I now turn it 90 degrees to where I am working and stick the loader into the ground. Never trust the BS parking brakes on tractors.