What if it was a UAV.... would you trust that parking brake?
Ths UAV still has someone at the controls. Bottom line is if the engines are running someone should have been in the seat, no reason to deviate from this.
On another note, the 747 classics were bad about this. The valve on the motor could get stuck while the condition lever on the pedistal would be in the "cutoff" position. I have once seen all three crew members just forget and walk out on all 4 motors running!