RenderMultiColumnSets were not patched correctly when RenderRegions became RenderBlocks. This bug is covering fixing the paint method to be more like RenderRegion's.
Created attachment 189165 [details] Patch
Comment on attachment 189165 [details] Patch View in context: https://bugs.webkit.org/attachment.cgi?id=189165&action=review > Source/WebCore/rendering/RenderFlowThread.cpp:254 > + // layout code that attempts to pixel snap will be incorrect. In general this is a huge problem with > + // subpixel layout (that attempts at snapping are just utterly wrong in the presence of any non-integral Perhaps you could omit this or say it in a more forward-looking way.
Fixed in r143395.