Yes like Adywan said, the ITV broadcast contains the genuine mono mix and not a stereo fold-down. One of those early ITV broadcasts was actually what was utilized when doing the mono restoration project. This is what destroys my theory...
I thought this early print variation could be traced to a difference between the early batch of Dolby prints vs. later batch of '77 prints. Prints with the mono mix didn't get out until June '77, that's when I thought this change occurred. But the ITV-broadcast contains the cloudy composite and mono mix - the first source encountered with that trait.
Could the audio and video be from separate sources? Mystery... ;)