OK, this exact situation has beed done to death a few times before and I've even asked the opinion of an international judge.
John, You don't know a case number for this incident do you??
My name is Simon, and no I don't have a case no; It was a protest that was heard (I believe) and all parties agreed after the fact as to what was going on.
Oops..Sorry Simon!! I may have found one good case that is relevant (I'm still looking for more..) Rule 14 case 92...
"When a right-of-way boat changes course, the keep-clear boat is required
to act only in response to what the right-of-way boat is doing at the time,
not what the right-of-way boat might do subsequently."
btw...all current Cases can be found at
http://www.sailing.org/rrs2005/casebook2005.pdfvery interesting read....