The tree's texture map is 54 by 12573 pixels(!), and it's a BMP, meaning 256 colors. No wonder, then.. :)

You can get the sphere looking proper by loading the bump map as a reflection map and inverting it. Yeah, it's a workaround.

With these renderspeeds it looks like I'll have to composite the shots, rather than rendering them all-in-one. I hope LightWave is up to it..