If an element has no -webkit-transform specified, adding it later on to scale it will result in severe underpainting. Happens in both Safari 3.1.1 and ToT.
Created attachment 21774 [details] reduction
Created attachment 25326 [details] Patch, testcase, changelog
Committed r38651 M WebCore/ChangeLog M WebCore/rendering/RenderObject.cpp A LayoutTests/platform/mac/fast/repaint/change-transform-expected.png A LayoutTests/platform/mac/fast/repaint/change-transform-expected.txt A LayoutTests/platform/mac/fast/repaint/change-transform-expected.checksum M LayoutTests/ChangeLog A LayoutTests/fast/repaint/change-transform.html r38651 = 1dffe8ff6fe257f4ed56ef33ea027dac44e9ef0a (trunk)