My gut is telling me that you may have that line on your right side graphic. Any amount of trans along the edge would show that, even if it's not very visible on the graphic. I would zoom in on that graphic in PS as far as possible, and see if there is any bit of trans on that edge.
Edit: I wouldn't mind having a closer look at the blind if you like....
Edit again: You making that with layers in SKS?
Edit again, again: Is there any animation on that? If so, perhaps it's on the animation layer?