This is common. Otherwise you get a mess of copyrighted code, and making it effectively impossible to determine who owns the copyright to what. Good luck if you

This is common. Otherwise you get a mess of copyrighted code, and making it effectively impossible to determine who owns the copyright to what. Good luck if you ever want to change the license or give one person a special license. You can use Project Harmony (http://harmonyagreements.org/ http://harmonyagreements.org/) to generate one of these agreements for your own project. It's targeted at FOSS, and the licenses themselves are under CC-AT-3.0.