I had a situation in RayDream which sounded similar. I had a waffled plate of glass (refractive) floating with a couple beveled pieces of glass floating in front of the waffled glass. When the beveled plate came in front of the waffled plate, all of the waffle refractions were cancelled, allowing the background to be seen without the waffling effect. This sounds like the same problem you're having. My solution was to render the waffled glass and background, then put this movie in the backdrop and render the beveled pieces over it. You might have to do similar layers. hope this helps.