background-attachment: fixed ignored when ancestor uses transform-style: preserve-3d
In a CSS3 layout, a section uses background-attachment: fixed on a large hero image. An ancestor element carries transform-style: preserve-3d to support a 3D card-flip effect deeper in the tree. Under that combination, the fixed attachment appears to be treated as scroll in some engines, so the background moves with the page instead of staying pinned to the
css3