2.2 Patent License [...] Microsoft and its Affiliates hereby grant Company [...] license under Microsoft's Necessary Claims to make, use, import, offer to sell, sell and distribute directly or indirectly to End Users, object code versions of Company Implementations only as incorporated into Company Products...

This appears to imply that Microsoft are not allowing you to distribute 'a BPEL implementation' but 'a BPEL implementation as part of another product'.

2.3 Source Code Distribution Company also has a nontransferable, non-sublicenseable, personal, license to distribute or otherwise disclose source code copies [...] only if Company [...] distributes or discloses the source code only under a license agreement that includes the following notice as a term of such license agreement and does not include any other terms that are inconsistent with, or would prohibit, the following notice:

"This source code may incorporate intellectual property owned by Microsoft Corporation. Our provision of this source code does not include any licenses or any other rights to you under any Microsoft intellectual property. If you would like a license from Microsoft (e.g. rebrand, redistribute), you need to contact Microsoft directly."

The non-redistribution clause goes against section 3 an 7 of the OSI definition of an open source license, so it seems unlikely that it would be possible to license a BPEL implementation in an 'Open Source' way.