When the PID output is OFF, no current flows to the motor, and no torque is applied in either direction."in response to positive PID output" - what happens if the PID output is "OFF" instead of a number?
When your motor is running away, the PID output is not OFF. It is either positive or negative, probably very briefly maxed out at +127 or -128. However, as soon as the runaway is detected, the control removes power from the axis and from the drive. By the time you take a picture of the screen, the output has reverted to OFF.
Try swapping the motor power leads on terminals 3 and 4 of the servo drive (i.e. swap Y+ with Y-). Then see if you can jog it without getting a runaway. Also see whether, when you do that, the axis jogs in the correct direction, or whether motion is reversed.