Known fault that if GREEN or YELLOW loses pressure due to fluid loss then the PTU starts BUT if there is only fluid on one one side then the PTU burns out causing the other system to leak out through the burned hole!!!
Our Company SOP is the to turn off the PTU without delay following the 'low pressure' of GREEN or YELLOW system. I think Airbus are working on a fix that this will happen automatically allowing the crew to make the decision about turning the PTU back on?
£10 says that this crew left the PTU running.