I actually figured out my issue last night. In case anyway else runs across this issue let me describe my scenario.
Configuration
1. Windows 7 x64 running VS 2010 (local). On this machine I am running NUnit tests that create a bus using the Service Bus Configurator.
2. Windows Server 2008 R2 running a topshelf hosted windows service (remote machine). The bus is configured the same as in the nunit test. The service acts as API over a non-unit testable resource
3. All buses are using Multicast MSMQ, no control buses.
4. Firewalls have ports inbound and outbound open for PGM.
Operations
1. I would start the service and would see Peer Messages appear in both the console output for the service on remote and appear in the subscriptions queue on local.
2. I would execute my nunit tests. The peer messages would be popped from the subscription queue and communication would proceed as expected.
3. If I would then immediately execute the tests again communication between local and remote would fail.
Resolution
1. It appears my local machine cannot broadcast multicast messages
2. I have had no problem sending multicast on a Windows Server 2008 machine.
3. I should note that the remote machine above is a guest hosted in virtualbox on the local machine so my issue appears to be specific to the Win 7 network stack or at least my configuration.