The vehicle was placed in 4 wheel drive (high range) and operated normally. Stopped the vehicle and placed it back into 2 wheel drive (indicated on dashboard as in 2 wheel drive). Placed transmission setting into "Park" but did not apply emergency brake. Turned off engine and exited vehicle. Vehicle proceeded to roll backwards down a slight hill until it crashed into tree (damage was limited to body panel). In summary, although the transmission was in park, it acted like it was in neutral. After several attempts of placing the vehicle in and out of 4 wheel drive, it did reestablish the Park mechanism. I have been able to recreate the situation with it continuing to fail.