Grace 707 tonearm wiring

Hi guys
I am a bit puzzled by the Grace 707 headshell wiring.
As per many pics online, the red (right hot) wire, when soldered to the shell is linked to a copper plate inside the headshell (shield, ground?). That copper is not connected to anything else but the finger guard. It means that if I do the wiring correctly, i have a hot wire linked to the finger guard and a loud hum/buzz when i grab the headshell by the guard!
Any idea as to the logic behind this kind of wiring?