Rich,
We had some discussions on this and finally decided to introduce a FlyTreeView.SelectNodeOnRightClick option that handles the case.
It is true by default, so you need to set it to false to make it work as you need.
A new version of the control containing this option was published few moments ago. Please download it from here:
http://www.9rays.net/download.aspx?productFamily=TreeView_ASP.NET_2