Seems like it’s the night for a braindump over the last couple of weeks…..

Hotfix 923632 will do the job.

Also
be sure to follow these steps after applying hotfix 923632:

 
1.  Open regedit and go to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\BTSSvc$<HostName>

 
Make sure host name is the name of the BizTalk host which is publishing messages which
are routed to multiple req/resp subscribers.

 
2.  At that key, add the DWORD value AllowMultipleResponses and set it to a value
of 1.

3. 
Restart the host service after making this change.