Created attachment 214199 [details] Testcase The testcase shows a bug (missing background image on the middle div) which I think happens because when we determine that an element can use the solid color optimization, we omit to check to see if any descendants render into it.
<rdar://problem/15224559>
A couple of things here: 1. I think this boolean logic in RenderLayerCompositor::requiresOwnBackingStore() is wrong: if (compositingAncestorLayer && (!compositingAncestorLayer->backing()->graphicsLayer()->drawsContent() || compositingAncestorLayer->backing()->paintsIntoWindow() || compositingAncestorLayer->backing()->paintsIntoCompositedAncestor())) return true; but fixing that would prevent having nested "paintsIntoCompositedAncestor()" layers. 2. isSimpleContainerCompositingLayer() gives the wrong answer if descendant compositing layers are "paints into ancestor" layers.
Fixed via bug 133065. *** This bug has been marked as a duplicate of bug 133065 ***