I had an A32 and it did turn itself off every now and again. Mostly it happened when I lived in a particular place, and the only place for my hi-fi was in front if a radiator. I think that when the radiator was on, the temperature raised to a point where the amp's protection circuit cut in - I expect Del Smith's problem was the same when the sun shone on his amp.
It would also switch off if there was an interruption to the mains supply, even if it was so brief that no other appliance would be noticably affected - I've come home a few times to find that it was entirely off when I had left it on standby.
A more 'out-there' theory along the same vein as the stray speaker wire could be the magnetic fields of speaker or mains cables in close proximity interacting to make the amp think there's a short and invoking it's protection mechanism - unlikely, but could be worth make sure everything is reletively tidy and not twisted/coiled together.