Having read this post about the Vienna video, I stumbled across an old copy of the Extreme Voice - EV20, in the Media Archives of this site.
There is a section in there where the band were questioned about what they could remember about the filming of the Vienna video.
Here's what Warren had to say about it.
"FILMING THE PARTY...
WARREN: It may come as a surprise to know that
approximately half of it was shot on locations in central
London, mainly at Covent Garden and also in the old
Kilburn Gaumont Theatre in North London (sadly, now
a Bingo hall). The ‘Embassy’ party scene was in some
house we’d rented in town – can’t remember where
but I do remember that it took the crew a long time to
set up the lights to prepare for filming... so long that
we all got impatient with waiting and dipped into the
many cases of wine we’d laid on for a drinkie
afterwards. By the time we actually started to film, we
were all rat-arsed. You know the bit where we're all
supposed to turn around at the same time, we just
could NOT do that in sync. Now you know why! In
between each take we were all at the booze again!
There was a lot of wine and not that many of us, so
you work it out... I had a lovely time".
Hopefully that solves the reason why some of the people couldn't turn in sinc with everybody else!