Same here at work, not that I model with tris anyway, butanywone who does gets their work back. Renderman likes it perfect. It doesnt mess about. No non manifolds or tris. But it was developed by Pixar as a subd renderer anyway (catmull- clarke), and what happens when you convert any mesh to a subd and back to poly? everything gets quaded - so theres the answer as to why it wants quads - I dont blame it though, tri are just a messy buggers LOL

Jay