Could you please elaborate a little bit more on your scenario because as far as we've tested the CanExecuteSave method is always called after shape drop ?
I've attached a sample project so you could examine it and tell us what you're doing differently.
Check out Telerik Analytics, the service which allows developers to discover app usage patterns, analyze user data, log exceptions, solve problems and profile application performance at run time. Watch the videos
and start improving your app based on facts, not hunches.