Stephen,
The first couple of production runs were built slightly different than later versions. The early version treated the HT pass through input differently in that it was passive (i believe) ie the Candela did not need to be powered on to work for HT PT. There were some issues so the later (current) version treats this input as active, just like the others.
Mine was an early version which I had Odyssey bring up to spec. Can't remember how much I paid, if anything, for the up grade. Probably best to PM AlexG and ask him directly.
Bob