Blueprint service factory does not implement required interfaces

Issue

I am trying to use ServiceFactory in blueprint to register a service and here is what the blueprint looks like:

<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0">
   <bean id="HelloFactory"  class="org.jboss.fuse.servicefactory.impl.HelloServiceFactory" />
   <service ref="HelloFactory" interface="orb.jboss.fuse.servicefactory.HelloService" />
</blueprint>

Where HelloServiceFactory is an implementation of org.osgi.framework.ServiceFactory to provide a service HelloService:

public class HelloServiceFactory implements ServiceFactory<HelloService> {

    @Override
    public HelloService getService(Bundle bundle, ServiceRegistration serviceRegistration) {
        return new HelloServiceImpl(bundle.getBundleId(), bundle.getSymbolicName());
    }

    @Override
    public void ungetService(Bundle bundle, ServiceRegistration<HelloService> serviceRegistration, HelloService helloSrv) {
    }
}

And HelloService is a very simple interface:

public interface HelloService  {
   public String say();
}

Obviously, HelloServiceImpl is an implementation of HelloService interface:

public class HelloServiceImpl implements HelloService {
   …
}

However, above blueprint gives an error when deployed to JBoss Fuse 6.1 container:

09:19:08,035 | ERROR | l Console Thread | ServiceRecipe | 9 - org.apache.aries.blueprint.core - 1.0.1.redhat-610379 | Error retrieving service from ServiceRecipe[name='.component-1']
org.osgi.service.blueprint.container.ComponentDefinitionException: The service implementation does not implement the required interfaces: [org.jboss.fuse.servicefactory.HelloService]