Created attachment 420859 [details] Test case The UseLocalClipRectIfPossible code path in RenderLayer::calculateLayerBounds() assumes that all descendants are affected by the clip, but that'd wrong; this layer might not be in the containing block ancestry of descendant layers.
I think it needs to call clipRectRelativeToAncestor() with the ancestorLayer all the way down, rather than resetting ancestorLayer at each level.
<rdar://problem/74753726>