java.lang.ClassCastException when returning an object in a Camel direct-vm invocation.

Issue

Running an application that connects two Camel routes using the Camel direct-vm component.
Both routes run as separate OSGi bundles.

Now, when the invocation to the direct-vm endpoint returns an object a ClassCastException is raised, similar to

13:59:11,742 | ERROR | qtp450940431-649 | DefaultErrorHandler | 130 - org.apache.camel.camel-core - 
2.10.0.redhat-60024 | Failed delivery for (MessageId: ID-mac-fritz-box-57446-1391517345547-8-2 on ExchangeId: 
ID-mac-fritz-box-57446-1391517345547-9-1). Exhausted after delivery attempt: 1 caught: 
java.lang.ClassCastException: com.mycompany.session.management.impl.SessionImpl cannot be cast to 
com.mycompany.session.management.Session

Both, the interface Session and the implemenation class SessionImpl are part of the bundle that consumes from the direct-vm endpoint.