See attached testcase. A element has a directly composited background that then intersects with its children layers. We either need to flatten (which might be incorrect if the container preserves3d) or turn off composited backgrounds in this case.
Created attachment 208051 [details] Test case
<rdar://problem/14637848>
This regression was caused by Bug 103786 and http://trac.webkit.org/changeset/137006