Hi there,

The problem appeared to be due to IE selection API and range (setStart, setEnd and select) which does not select/highlight the HTML elements having applied contentEditable attribute. 

The only possible workaround is to replace the contenteditable attribute with _contenteditable when opening the dialog in the OnClientCommandExecuting event of RadEditor, and return back the original attribute from _contenteditable to contenteditable when closing the dialog. For your convenience I developed a solution which you can apply to its project:


<script type="text/javascript">
    function OnClientCommandExecuted(editor, args) {
        if ("FindAndReplace" == args.get_commandName() && Telerik.Web.Browser.ie) {
            editor.set_html(editor.get_html(true).replace(/contenteditable/gi, "_contenteditable"));
            alert(editor.get_html(true));

            //Get reference to parent RadWindow
            var wnd = Telerik.Web.UI.RadWindowController.get_activeWindow();


            //When closing the dialog
            var handler = function (sender, args) {
                //Restore the original contenteditable attributes
                editor.set_html(editor.get_html(true).replace(/_contenteditable/gi, "contenteditable"));
                alert(editor.get_html(true));
                //Remove the close handler
                wnd.remove_close(handler);
            }

            wnd.add_close(handler);
        }
    }
</script>

<telerik:RadEditor ID="RadEditor1" runat="server" OnClientCommandExecuted="OnClientCommandExecuted">
    <Content>
        <p>test</p>
        <p contenteditable="false">line one</p>
        <p>line two</p>
        <p contenteditable="true">line three</p>
    </Content>
</telerik:RadEditor>