I always wondered:

I have never ever personally seen shorted RCA plugs for sale.

But, I have seen the Canare caps (?) many times. All these do, is to basically metallicly cover the jack. (Wraps the shield over and around the inner conductor without touching it.) But not shorted between the center condutor and the shield.

I always thought that inputs were meant to see ~50 - 75 ohm impedance. Shorted plugs? That's 0 impedance.

But I'm no EE...