Hi Martin,
You said that when you attached a Lambert shader at the end, the problem didn't persist. That means there must be some point at which the problem comes back if you move the shader back one by one. If the problem re-emerges after moving it so there is only one shader after the Lambert or Constant shader, then that means the problem can be caused by that very last shader.
Send me the .tgd when you get a chance and I will take a look.
Matt
