When rotating a window there is obvious aliasing at the window edges. This would typically be resolved using MSAA but this is not really an option due to the complexity that this would involve for the renderers and the reduced performance that would result from that. As a solution I suggest to extend the rendering surface of all AutoRenderingSurfaces by one pixel to the left,right,top,and bottom and rendering the viewport to the original unextended area, efficiently leaving 1 pixel empty at the border.
This wouldn't work for closed 3D objects, but in our case our object is completely planar so the outer edge is always the same. Resolving the aliasing issue would then be transferred from a geometry-level to a texture-level, and texture-aliasing is comparatively easy and already done in CEGUI.