[away3d] Broomstick CubeMap SkyBox corner tearing / artifacts

[Choons]

I've noticed an issue a few times now with CubeMap Skybox's in
Broomstick where at certain angles when the camera is looking at the
corners of the sky it appears as if the corner has been cut off and a
black triangle shows through. I first noticed it in the
SimpleTerrainTest example and am now seeing it in a project I'm
working on. I've added a background color to the view to try to match
my sky color but it's still noticeable. Anyone know how to fix that?