Does this tractor have hydraulic operated brakes? If yes, how can you do a emergency braking if you looses the main brake?Yep, I think park means park. It should not move.
The foot brake does not lock on the 12 speed model.
Sharing your experience is great. But you do not seem to have thought through the ramifications of your actions fully, in order to make tractor operation safer in the future.
Everything you needed to prevent the rollback was there. You failed to turn off the engine and lower the FEL bucket.
THE ENGINE SHOULD HAVE BEEN OFF. You should realize this by now.
OP's tractor must have something out of adjustment.