[Papervision3D] MovieMaterial -No Interaction if source not visible on stage

[-a-]

This is a puzzler, I have a Flex list control which is part of a 
MovieMaterial source. The 3d primitive interactsROll-Overs, Clicks, etc) 
properly if its within the stage boundaries but, move it to say y = -200 
and BAM no more interaction. Same it seems if you set the 
movieclip.visible to false. Can any one explain why this would happen?

a/