@thomthom said:
But I haven't been rendering with Alpha. It's been all without.
I had a chance to look at it some more. You're right, alpha was not on - but it still rendered areas without geometry as black. I tried the "z-depth catcher" plane - and it does work in making the background white. I did a quick check- and if the plane is beyond the rear clipping distance, it still shows up as white, so I assume that anything that's clipped by vray is drawn as white, but anything transparent is shown as black.
I agree that it's really not an optimal situation. It should clip the foreground to black, the background to white, and draw transparency as white (to assume that you are looking at the back distance...)