not to throw a large monkey wrench (how many of you folks are old enough to know what a monkey wrench looks like... raise your hands) into everyone's thinking, I keep recalling an incident from about 20 years ago that keeps coming to mind with the ccd thingee. we (I was working for a commercial concern then) had a fellow set down next to us in east texas who (if memory serves) was a small commercial outfit from south dakota. all during the spring his bees never really took off, matter of fact some dwindled even though they seemed well provisioned. if the owner had seen the same bees, seperated by about 2 weeks, I would think the symptoms would have looked much like ccd (or whatever you might wish to call it this time). it seems he had made some tops out of some form of treated plywodd and the bees were being slowly gassed everytime the wood was exposed to rain or water.
I guess why this come to mind is the odd symptom that the hives affected were not robbed out until the top is removed and the equipment is air out for a couple of days. sounds like some low level 'gas' would almost have to be present to mask the honey smell from all those unprotected hives especially in a commercial hive setting.