At the moment, my code is using a RenderQueueListener and I'm hooked into the Overlay ID on renderQueueStarted().
This is what I expect (image taken with Ogre 1.6 and CEGUI 0.6.2):

This is what I get witout doing anything apart from showing the console:

And this is what it looks like after focusing the first button:

I also checked to see what happens if I hook into renderQueueEnded --> as expected, I cannot see anything at all.
Any ideas how this could happen?