Site is only working with .COM?

It seems to me that when I added a url to Site it does not recognize a web site that is not ending with .com. It works OK with a url ending with .com is submitted but when a URL ending like .us it says

This link does not appear to be a working link. Please check the URL and try again.

It seems like it is recognize it when there is a back slash at the end of the URL.