My wife had this the other day in the the Leon and to me it seemed that she was putting it into gear and immediately hitting the accelerator, as in hitting the gear shift as she lifted from the brake to the accelerator. This was reverse on a slight incline. Every time it went into park and the handbrake came on.
In my case I don't do that - I put it in gear then release the brake but don't hit the accelerator as it's on a hill anyway so starts moving. When she did the same it didn't happen.
Mibbe it's a timing thing. (No expert and this is only my 2nd automatic)