[Stuart]

Strange that that would make it to air with the copyright caption as well

The News Channel UK feed did broadcast something on their schedule slated as 'BBC News at Six', and at the end probably just switched to B's gallery in preparation for the '7'. 

If the regions didn't opt out in time they would have caught it, but it seems odd that there was a copyright caption unless that was the end of a rehearsal.

Sophie would probably have been there as usual from about 17:30. As the start of the delayed national bulletin wasn't confirmed until quite late, there would be little point in her moving as she can presumably achieve any script changes from the desk in B as easily as going back up to the newsroom.