The value set to the EmptyMessage of the editor floats outside the EDitor if its length exceeds the Editor's width - http://screencast.com/t/rPLVwFVfU

When the Editor is used in Right to Left mode, the modules at the bottom of the control are not properly positioned and the resizing handler does not point to the right direction - http://screencast.com/t/JwPlpE3zPDzi

When creating links in RadEditor if the href attribute has square brackets, opening the hyperlink manager will appear like there is no url at all. 
If OK button is clicked the url disappears.

When the property 'AutoResizeHeight' is set to 'true' and 'ContentAreaMode' is set to 'Div', the appearance of RadEditor will be distorted in IE10. Also, the height of the editor is reduced the first time HTML view is selected under IE10 and older versions when the same setup is used.

RadEditor uses a RadWindow for its dialogs so when the global rendering of RadCocntrols on the page is set to Lightweight the dialogs need to be consistent.
There could be implemented a property to control the RenderMode of the dialogs themselves.

The Bold, Italic, Underline, Subscript and Superscript commands do not work in a combination with EnableTrackChanges="true" and ToolbarMode="RibbonBar".

When hyperlinks are inserted into the content of RadEditor in preview mode there are additional attributes , which are retrieved by the get_html() method. 

If the MaxHtmlLength is set and the content is close to the limit on switching to preview mode breaks the normal behavior of the editor. The validator alerts that the length is exceeded, because of the additional attributes and the client is not able to open any other mode.

A possible workaround:
<rad:RadEditor ID="RadEditor1" runat="server" OnClientCommandExecuted="OnClientCommandExecuted"></rad:RadEditor>
function OnClientCommandExecuted(editor, args) {
                if ("Unlink" == args.get_commandName()) {
                    if ($telerik.isFirefox) {
                        var anchor = editor.getSelectedElement();
                        if (anchor && anchor.nodeName == "A") {
                            Telerik.Web.UI.Editor.Utils.removeNode(anchor);
                        }
                    }
                }
            }  

Ability for the RadEditor's validator dialog to validate HTML 5 markup inside it's content

Telerik version 2011.1.614.35
I am facing following two issues with RadEditor on Chrome (version 28.0.1500.95) and Safari (version 5.1.7) -

a. Gray area is seen in the lower part of the RadEditor for Design and Preview modes. When some text is typed, the gray background vanishes for that line of text. 

b. Border of the RadEditor is not complete at the bottom left corner in the HTML mode. This behavior is seen whenever there is some text in it, be it the default text or the text of the field that is bound. 

Please refer the attachment RadEditorIssues.png 

When opening a RadEditor under Chrome and switch to HTML mode in the bottom left corner, close to the Design title there is missing a small part of the border.

RadEditor's content is messing up when links are generated through document manager and submit it from Preview mode. The issue is reproducible in Internet Explorer 7

However, a possible workaround for the issue would be to set the following code the OnClientSubmit event of the RadEditor:

<telerik:RadEditor OnClientSubmit = "OnClientSubmit" />
 
<script>
   function OnClientSubmit(editor)
   {
   editor.set_mode(1); //Force design mode
   }
</script>

The Insert Web Part tool in RadEditor for SP 2010 throws JavaScript error (reproducible in all browsers).

Steps to reproduce:
1. Open http://sharepoint.telerik.com/aspnet-ajax/web-parts/Pages/Content-Editor-Web-Part-using-RadEditor.aspx
2. Click over the content of the Editor, so the toolbar will be shown
3. Click over the Insert Web Part Tool

video - http://screencast.com/t/Df3aV6svUy

When navigating inside a table in the RadEditor, pressing the right arrow key of the keyboard moves the cursor only till the last table cell and the cursor does not exits the table. 

When multiple instances of RadEditor are placed inside hidden ASP Panel (visible='false') which is ajaxified with RadAjaxManager/RadAjaxPanel, and then the visibility of the ASP Panel is switched to true, the Statistics Module of the second, third.. Editors display 'undefined'. The issue is observed under Internet Explorer.

The workaround is to use:

-either ASP:UpdatePanel instead of the RadAjaxManager/RadAjaxPanel

-OR use the following JavaScript override:

            Telerik.Web.UI.Editor.Modules.RadEditorStatistics.prototype.doCount = function () {
            
                if (!this.get_visible()) return;

                var content = this.get_editor().get_text();

                var words = 0;
                var chars = 0;
                if (content) {
                    var punctRegX = /[!\.?;,:&_\-\–\{\}\[\]\(\)~#'"]/g;
                    content = content.replace(punctRegX, "");
                    var trimRegX = /(^\s+)|(\s+$)/g;
                    content = content.replace(trimRegX, "");
                    if (content) {
                        var splitRegX = /\s+/;
                        var array = content.split(splitRegX);

                        words = array.length;

                        var newLines = /(\r\n)+/g;
                        content = content.replace(newLines, "");
                        chars = content.length;
                    }
                }

                var elem = this.get_element();
                elem.innerHTML = "<span style='line-height:22px'>" + "Words:" + " " + words + "   " + "Characters:" + " " + chars + " </span>";
            }

In order to make the above function override working, it must be placed:

-Either below the RadScriptManager and load all the necessary resources through ScriptReferences of the RadScriptManager (disable the embedded resources of the RadEditors' instances too)

-OR create an additional instance of RadEditor in a hidden div, outside the AjaxPanel and place the function override below it.

When the content of the editor is within a SPAN element, nested in a P, pasting data with P element inside it using the pasteHtml() method throws JavaScript errors and the SPAN element is broken by the nested P elements.

Steps to reproduce:
1.Set editor's content with this content: <p><span>Some text</span></p>

2.Use the editor's pasteHtml() method to paste this HTML in the middle of the above text: <p>Second text</p>

3.The result HTML is this:
<P><SPAN>Some</P>
<P>Second text</P>
<P>&nbsp;text</SPAN><SPAN>​</SPAN></P>

 

When a RadEditor control is set to a small height and ContentAreaMode='DIV' resizing the wrapper causes the size calculation functionality to break, because the calculated value is negative.  

The resize handles of the ImageEditor's drawing tools are displaced when the edited is zoomed (both zoomed in or out).