First, can you clarify exactly which variant of Fender Deluxe Reverb you have? This may appear on the amp chassis or on a label near the loudspeaker. It will definitely appear on the schematic circuit diagram.
it happens to all of my marshalls too. it's annoying. i've found some strange ways to mitigate it. it's a combination or all of the below:
-turn the volume all the way down on the guitar
-turn the volume all the way down on the amp
-let the amp sit idle for a couple of minutes before you put it on standby. put the guitar volume all the way down.
-flick the standby switch quickly
-ground yourself when you touch the standby switch
i'm wondering how much damage it does to the speakers.