title: Pub/Sub not working between NServiceBus 4.3 and 3.3 endpoints
body: <p>We are in the process of upgrading <code>NServiceBus</code> from 3.3 to 4.3</p>
  
  <p>We've got 2 <code>NServiceBus</code> endpoints of different versions.
  One is the publisher(still using version 3.3) and one is the subscriber(using new 4.3 version).
  The subscriber is using Bus.Subscribe method to subscribe</p>
  
  <p>What we see is that publisher is receiving subscription messages into its queue with the <code>NServiceBus.MessageIntent</code> equal to Subscribe in its header.
  When processing these subscription messages publisher(version 3.3) is unsubscribing instead.
  Here is what we see in the logs</p>
  
  <p><code>NServiceBus.Unicast.BackwardCompatibility.IncomingSubscriptionMessageMutator [(null)]</code> - Just mutated V3.0.0 to message intent: Unsubscribe</p>
  
  <p>Any help would be appreciated as we are blocked on our <code>NServiceBus</code> upgrade at this point.
  We actually are forced to upgrade all of our Pub/Sub pairs of endpoints.... Can we avoid doing that somehow ?</p>
  
  <p>Thanks. Any help would be appreciated.</p>