Personally I always connect up the backs of my pot casings, but I also cut a plastic guard out of milk bottle for each and every pot to make sure the lugs can't contact the shielding. It's basically a wierd shaped washer that corresponds to the underside profile of the pot, with a hole for the shaft to stick through. I'm happy to take a little extra time connecting the pot casings if it means I dont have to troubleshoot shorts with the lugs!

cheers,
Gav.