RadEditor in Fullscreen mode appears cut off at the right and at the bottom. 



In order to fix that, you can add this CSS rule to the page:

<style>
    .RadEditor.reFullScreen {
        box-sizing:border-box;
    }
</style>

<telerik:RadEditor ID="RadEditor1" runat="server" RenderMode="Lightweight">
</telerik:RadEditor>