The click event of the button is not prevented and the native anchor behavior occurs. This causes the page to scroll to the top and a # to appear in the URL. 

You can use the following code snippet to prevent the native click behavior of the anchor element and workaround the issue:

<telerik:RadEditor runat="server" ID="RE1" ToolbarMode="Floating" OnClientLoad="OnClientLoad"></telerik:RadEditor>

<script>
    function OnClientLoad(sender, args) {
        $telerik.$(".RadEditor a[title='Toggle Floating Toolbar']").attr("href", "javascript:void(0);")
    }
</script>