To reproduce: 1. Go to http://annevankesteren.nl/ 2. Make the window more than 2000px wide 3. Hover over the sidebar links When the hover animation occurs, the "SVG SUCKS" text in the sidebar shifts upwards by one pixel. It shifts back into place when the animation finishes.
The page enters compositing mode for the duration of the animation. When the window is more than 2000px wide, we used a tiled layer for WebView::m_backingLayer.
<rdar://problem/8876819>