Hey freakpear, no problem.
A few things:
What it looks like to me is that the image is on a 'higher' layer than the header. Because your header is pinned you want it to be on the highest layer possible so that it will 'slide' over everything:
Second it looks like you placed an image or you set the WHOLE box on scroll motion. What you want is a rectangle, filled with and image. From there you go to the SAME menu that you set the fill, but click 'scroll' not scroll effects. Then you want to set all the attributes to 0 except key position.
Let me know if it works!
Here is my demo: Home