Microsoft is clearly taking something of a"copy left" approach to Shared Source, an approach that is used widely in the real open source community.
Here is the copyleft section:
If you distribute the larger work as a series of files, you must grant all recipients the copyright and patent licenses in sections 2(A) & 2(B) for any file that contains code from the software. You must also provide recipients the source code to any such files that contain code from the software along with a copy of this license. Any other files which are entirely your own work and which do not contain any code from the software may be licensed under any terms you choose.