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]
Comment on attachment 189165 [details]
View in context: https://bugs.webkit.org/attachment.cgi?id=189165&action=review
> + // 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.