Instead, there should be (throughout the stack from WKView to TiledCoreAnimationDrawingArea) another property that clipsToExposedRect/shouldClipToVisibleRect should be keyed off of, instead of main frame scrollability.
<rdar://problem/14301175>
Created attachment 205686 [details] preliminary
Created attachment 205737 [details] patch
http://trac.webkit.org/changeset/152190