So, it must be to do with the two renders then.
I don't think so ... it's the shadows which use two renders to texture. If I turn them off completely then same problem. I don't think only doing this once will make a difference ... besides I need both renders.
Oh, and I'm not using entityorder on any mesh in the game - I know that disables z-order.
Unless anyone has any further suggestions then I'll see if others experience the problem and package up a quick demo for the weekend.
Thanks to everyone for their advice and help so far. Still racking my brains about this!!
Stevie