If a layer of foam is still attached to the fiberglass, then I would think that it is not an adheasion problem. I would guess that the shear stresses in the foam exceeded the strength of the foam and the dust is from the two surfaces rubbing together each time the skin flexes. This is only a guess but you test the idea by cutting out a strip from an area that is not seperated and bending it back and forth several times to see if it will cause a failure similar to what you see in the picture.