Apply a RoundRectShape with Radius 25 to the RootElement of a RadPanel and set panel's BackgroundShape property. Note that the image is not clipped with the correct 25 radius.

Workaround: to avoid the issue through resetting the ApplyShapeToControl property when the panel is resized.
 void radPanel_SizeChanged(object sender, EventArgs e)
        {
            RadPanel panel = sender as RadPanel;
            if (panel != null)
            {
                panel.RootElement.ApplyShapeToControl = false;
                panel.RootElement.ApplyShapeToControl = true;
            }
        }