Well, this say exactly what the title says. I think that when you click:
The system should tell you exactly which site(s) have different information than you have listed, and what would be over-written should you continue. Additionally, I believe that a confirmation success message should considered. IE:
Your profile information has been copied to all Stack Exchange network accounts.
Right now there's no indication that it's complete, and sometimes it doesn't even appear to work (due to browser caching and other complications.)
Sorry for the huge images, that's the zoom I have to use to see StackExchange :(