LH question involving the sky background

[cfkane]

So, I'm working on a new leaderhead, and in a weird move, I'm trying to place the animated sky texture in front of the leaderhead itself, because I'm trying something out involving the scrolling animation. But whenever I do, the entire scene starts slowly shifting to the left, as if the sky was dragging the camera as it scrolled from right to left. For some reason it worked fine when I used a background that scrolled from left to right.

Any hypotheses as to what's going on?