Apperantly the Pro-SD back for the RB has a multiple exposure safe guard lock that has to be switched off to do multiples. I've done the "opps" a few times myself (I only have Pro and Pro-S backs). My Yashica TLR also makes one become a creature of habit. I've taught myself to wind the film back immediately after the exposure. Before I do anything else. Like cock the shutter, think (my worst downfall), put the lens cap back on, look at the bikini girls, move the tripod.
Now I multi-exposure by accident rarely, maybe once every 4-5 rolls.