OSGi Collection Listener Called Twice for Phantom Unregistrations

Hey,

There seems to be a bug in Spring DM 2.0.M1. I have a collection listener defined as such:

<osgi:set id="activeWorlds" cardinality="0..N" interface="test.World">
<osgi:listener bind-method="register" unbind-method="unregister" ref="worldRestExporter" />
</osgi:set>

When the application is started the unregister method is called twice with null as the parameter. I can't imagine why this happens or what it might mean and I can code around it but it is a little strange.