Possible option is to use the ToolsFile property from the code behind in order to configure a ToolsFile.xml file. 

RadEditor1.ToolsFile = "~/ToolsFile.xml";

Currently, the font family will not be passed to the Editor content. It's reproducible when loading tools from xml file. Possible workaround is to use ContentAreaCssFile to set such style or on the OnClientLoad event:

    <script>
        function OnClientLoad(sender, args) {
            sender.get_contentArea().style["font-family"] = "Arial, Verdana, Tahoma";
        }
    </script>

When part of a table from MS Excel is copied and pasted into RadEditor under Edge, the RadEditor inserts an image instead of the html for the table. It inserts <img alt="" src="data:image/png;base64, ... " /> instead of the html.

Steps to reproduce:

Open http://demos.telerik.com/aspnet-ajax/editor/examples/overview/defaultcs.aspx in MS Edge.On the editor select the html and delete everything.
On the editor select design
Open any Excel file copy a couple of cells
Paste in the Editor
On the editor select html
Instead if html the there is an image tag
<img alt="" src="data:image/png;base64,iVBOR ... YII=" />

With firefox, IE 11 and Chrome the html is pasted. For MS Edge the Image tag is pasted.

Workaround:
<telerik:RadEditor runat="server" ID="RadEditor"></telerik:RadEditor>
<script>   
    Telerik.Web.UI.Editor.Utils.containsHtmlAtClipboard = function(oEvent) {
        var result = oEvent && oEvent.clipboardData && oEvent.clipboardData.getData &&
            oEvent.clipboardData.types && oEvent.clipboardData.types.length &&
            Telerik.Web.UI.Editor.Utils.containsElement(/text\//i, oEvent.clipboardData.types);
 
        return result;
    }
</script>

Problem:

In the RadEditor we have the NewLineMode set to Div
We are also using a ToolsFile xml document to control the tools available in RadEditor.
The problem is the InsertParagraph tool now inserts <div> tags instead of <p> tags.
We want to keep the NewLineMode behavior as DIV while still having a tool that can insert a paragraph (i.e. a <p> tag).

To replicate this problem:

On the RadEditor demo page, first set "NEW LINES AS" to "Divs".
Then, in the editor content area just above the "Destinations" table, Type in three lines:
Comment1
Comment2
Comment3

If you then toggle to the HTML tab, you will see that the Comment1 line is (incorrectly) bracketed by a <p> tag while the Comment2 and Comment3 lines are (correctly) bracketed by <div> tags.

Next, go back to the Design tab and position yourself at the beginning of the Comment3 line then click the [Insert Paragraph] button.

In the newly inserted "paragraph" type "Comment2b".

If you then toggle to the HTML tab you will see that Comment2b is incorrectly bracketed by a <div> tag.  It should be a <p> tag.

In R3 2016 SP1 when a RadEditor with RenderMode=Classic is disposed and RadScriptManager is used, a JavaScript error is thrown:
IE:  Object doesn't support property or method 'dispose'
Chrome: Uncaught TypeError: this._contextMenuFunctionality.dispose is not a function

FIXED in R3 2016 SP2 (2016.3.1027)

There are three workarounds:
- Set EnableScriptCombine to false for the RadScriptManager (not applicable when CDN is used)
- OR set RenderMode=Lightweight for the RadEditor (you can do this in the web.config for all control instance in the web app if they do not define the Classic mode exiplicitly)
- OR add the following function override at the end of your page:

			<telerik:RadScriptManager ID="RadScriptManager1" runat="server" >
			</telerik:RadScriptManager>

			<%-- WORKAROUND 1: SET EnableScriptCombine="false" TO RADSCRIPTMANAGER--%>

			<asp:Button ID="Button1" Text="click to postback and break the editor" runat="server" />

			<telerik:RadEditor ID="txtInstructions" runat="server">
			</telerik:RadEditor>

			<%-- WORKAROUND 2: SET RenderMode="Lightweight" TO RADEDITOR--%>


			<%--WORKAROUND 3: ADD THE FOLLOWING SCRIPT TO THE END OF THE FORM--%>
			<script>

				Telerik.Web.UI.Editor.DefaultToolAdapter.prototype.dispose = function ()
				{
					delete this._fakeToolbarParentCreated;
					var toolbars = this._getToolBarElements();
					if (toolbars) {
						for (var i = 0; i < toolbars.length; i++) {
							$clearHandlers(toolbars[i]);
						}
					}
					this._tools = [];
					this._disposeToolbarModeHandlers();
					var wnd = this._toolbarHolder;
					if (wnd && wnd.dispose) wnd.dispose();
					var contextMenuFunctionality = this._contextMenuFunctionality;
					if (contextMenuFunctionality && contextMenuFunctionality.dispose) contextMenuFunctionality.dispose();
					Telerik.Web.UI.Editor.DefaultToolAdapter.callBaseMethod(this, "dispose");
				}
			</script>

Thead and tfoot elements get deleted with deleting content of table in Google Chrome.

On the RadEditor demo page [http://demos.telerik.com/aspnet-ajax/editor/examples/overview/defaultcs.aspx]

Replace the content with a table with a thead tbody tfoot caption

<table>
   <caption>ABC</caption>
   <thead>
      <tr>
         <th>A</th>
         <th>B</th>
         <th>C</th>
      </tr>
   </thead>
   <tfoot>
      <tr>
         <td>FOOT</td>
         <td>FOOT</td>
         <td>FOOT</td>
      </tr>
   </tfoot>
   <tbody>
      <tr>
         <td>A1</td>
         <td>B1</td>
         <td>C1</td>
      </tr>
      <tr>
         <td>A2</td>
         <td>B2</td>
         <td>C2</td>
      </tr>
      <tr>
         <td>A3</td>
         <td>B3</td>
         <td>C3</td>
      </tr>
   </tbody>
</table>

Select some content across the tbody, tfoot, thead and caption and delete 

Expected results: the content of the TD and TH should be remove

Actual results: the THEAD and TFOOT elements are removed

More details check the attached delete_thead_tfoot.gif file.

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

<script>
	(function () {
		var $E = Telerik.Web.UI.Editor;
		var utils = $E.Utils;
		var cmdPrototype = $E.DeleteSelectionCommand.prototype;
		var shouldCollectNode = cmdPrototype.shouldCollectNode;
		cmdPrototype.shouldCollectNode = function (node) {
			return shouldCollectNode.call(this, node) && !utils.isTag(node, "thead") && !utils.isTag(node, "tfoot");
		};
	})();
</script>

The context menu for IMG and Table element immediately hides when shown on Mac Firefox.

Load this demo http://demos.telerik.com/aspnet-ajax/editor/examples/overview/defaultcs.aspx on Firefox Mac OS
and right click in a table cell or image. You'll see how the menu pops up and immediately closes.

Video reproduction -> http://www.screencast.com/t/osHP96eQOa7

In IE, create a table and add a caption

Apply the style="display: none" to the caption

Attempt to select table using the Editor's select table function and an unspecified error is thrown in the console

This issue was reproduced on the RadEditor demo page.

This issue only happens in IE, could not reproduce in Firefox or Chrome.

This issue does not occur when the display: none style is removed from the caption.

Video: http://www.screencast.com/t/QxHb25w6e

RadEditor strips urls pointing to the current page when MakeUrlsAbsolute is enabled.

Steps to reproduce:
1. Open http://demos.telerik.com/aspnet-ajax/editor/examples/builtincontentfilters/defaultcs.aspx

2. Clear the content of the Editor, swith to html mode and paste the following content:
test
<a href="http://demos.telerik.com/aspnet-ajax/editor/examples/builtincontentfilters/defaultcs.aspx" target="_self">2.2.2</a>
<br>
<table bordercolor="#000000" border="1" cellspacing="0" cellpadding="2">
    <tbody>
        <tr>
            <td style="text-align: center; vertical-align: middle;" rowspan="2"><strong>Text</strong></td>
        </tr>
    </tbody>
</table>


3. Switch to Design mode and back to html mode.

Result: The content will be stripped like follows:
test
<a href="#000000" border="1" cellspacing="0" cellpadding="2">
     
         
            <strong>Text</strong>
         
     
</a>

There is a problem in Safari on Mac while selecting Table cell properties via the context menu when a table cell is selected. Its Wrongly selected in the Table Wizard window.

Reproduction steps:

- Load the default demo in Safari Mac: http://demos.telerik.com/aspnet-ajax/editor/examples/overview/defaultcs.aspx

- Right click over the third cell in the second column ("Los Gigantes is located...") and choose Cell Properties.

- The Preview of the Cell Properties in the Table Wizard will show that the first cell is selected but not the right one.

The Table Wizard dialog, the Table Properties tab shows Cell Padding and Cell Spacing fields, but this fields can only apply values. If you edit them through the HTML mode or the Properties Inspector module, the fields in Table Properties dialog will not be updated.

You can create a list item, but it is impossible to type text in the list item.

Steps to reproduce:
1. go to demo url http://demos.telerik.com/aspnet-ajax/editor/examples/edittemplate/defaultcs.aspx
2. click add new record
3. try to manually resize editor. it won't.
4. click add new record again.
5  try to manually resize editor, now it will.

Workaround is to add the following function override at the end of the page (a sample is attached below)
				Telerik.Web.UI.Editor.Utils.isWindowDestroyed = function (window) {
					var doc;
					try{
						doc = window.document;
					} catch (e) {
						return true;
					}
					if(Telerik.Web.Browser.safari && !doc){
						return true;
					}
					return !doc.defaultView && !doc.parentWindow;
				}

Several JS errors are trown when writing in re-focussed empty Editor in Chrome.

Video:  https://www.screencast.com/t/Wx6Ucs8m6S5w

First error's message:
RadEditor.js:10521 Uncaught TypeError: Cannot read property 'startContainer' of null


Steps to reproduce:
1. Open in Chrome: http://demos.telerik.com/aspnet-ajax/editor/examples/trackchanges/defaultcs.aspx
2. Switch to HTML mode and clear the whole content
3. Switch back to Design mode
4. Click any of the Bold/Italic/Underline commands
5. Click out of the Editor's element
6. Click back in the Editor's content area and start typing

Result: JS errors are thrown

http://demos.telerik.com/aspnet-ajax/editor/examples/overview/defaultcs.aspx
Clear content;
Add a table;
Open context menu by selecting a cell in the table;
Open Cell Properties;
Open More cell Styling;
Chose Background color;
Change it and click OK
Click OK in Table Wizard.
Actual: No background color is applied. 

The Bold, Italic, Underline, Justify, Indent, Outdent and other commands are not localized in the Undo/Redo dropdowns.

Screenshots:

https://www.screencast.com/t/YLNTiPP7LAk

https://www.screencast.com/t/DS9Y6GrB 


Can be seen at http://demos.telerik.com/aspnet-ajax/editor/examples/localization/defaultcs.aspx. 

When RadEditor is configured with RenderMode="Auto", it renders fine on a mobile, but the Find and Replace throws a JavaScript error:

Uncaught Error: Sys.ArgumentNullException: Dialog Parameters for the FindAndReplace dialog do not exist

Parameter name: dialogName
    at Function.Error$create [as create] (ScriptResource.axd?d=drtcXVcvAjvxxGTIp4ks_jsffAtTgDZa7F-xsErOE7x83oPLnSroIDP2Rlpln027LL6pHm8wDFlVd2TfNwyX9tsTD0IfApyfv4p2GRpAUsfag9bRTF3ZhqYQPg2KFASuXMmfKVcURGhOxnF7S60OLuj9cWAWD2oOw-AOIsKJVpoN8aJcHQVfLpfuW8e9J_z70&t=74693645:237)
    at Function.Error$argumentNull [as argumentNull] (ScriptResource.axd?d=drtcXVcvAjvxxGTIp4ks_jsffAtTgDZa7F-xsErOE7x83oPLnSroIDP2Rlpln027LL6pHm8wDFlVd2TfNwyX9tsTD0IfApyfv4p2GRpAUsfag9bRTF3ZhqYQPg2KFASuXMmfKVcURGhOxnF7S60OLuj9cWAWD2oOw-AOIsKJVpoN8aJcHQVfLpfuW8e9J_z70&t=74693645:279)
    at b.RadDialogOpener._getDialogDefinition (ScriptResource.axd?d=CcXTXAXm_2uXk6i-z8e-9-GUON7JgJld7fON2waeoUCDG-568SfljYE0OxAYq5S_l1j5QbPdt7yR5Ji7ARrlqe9xsoWPpTVgVVnsC2r0rN-hCMOIKe3sXa-glZDwstuHDCKnEGv03WuBZg3A1mEmGb3cZzVnLPok8zmI9TSFWuc1&t=6e6e42a6:199)
    at b.RadDialogOpener.open (ScriptResource.axd?d=CcXTXAXm_2uXk6i-z8e-9-GUON7JgJld7fON2waeoUCDG-568SfljYE0OxAYq5S_l1j5QbPdt7yR5Ji7ARrlqe9xsoWPpTVgVVnsC2r0rN-hCMOIKe3sXa-glZDwstuHDCKnEGv03WuBZg3A1mEmGb3cZzVnLPok8zmI9TSFWuc1&t=6e6e42a6:65)
    at c.RadEditor.showDialog (ScriptResource.axd?d=wYaAc3J2NgVJCu2P39J4xyGaoOdrMcpsgItEXwZ_xZ-mxwwqth9gFwZgQmz64y0L50bOGm0jxdnTOv_b92sCumvlnrhdNCqVSpfDTXuridpdeelSxC1ktLGb8SRXNUQSfAkHpn5XxFbvggex9gxJzw2&t=6e6e42a6:8753)
    at Telerik.Web.UI.Editor.CommandList.FindAndReplace (ScriptResource.axd?d=wYaAc3J2NgVJCu2P39J4xyGaoOdrMcpsgItEXwZ_xZ-mxwwqth9gFwZgQmz64y0L50bOGm0jxdnTOv_b92sCumvlnrhdNCqVSpfDTXuridpdeelSxC1ktLGb8SRXNUQSfAkHpn5XxFbvggex9gxJzw2&t=6e6e42a6:5051)
    at c.RadEditor.fire (ScriptResource.axd?d=wYaAc3J2NgVJCu2P39J4xyGaoOdrMcpsgItEXwZ_xZ-mxwwqth9gFwZgQmz64y0L50bOGm0jxdnTOv_b92sCumvlnrhdNCqVSpfDTXuridpdeelSxC1ktLGb8SRXNUQSfAkHpn5XxFbvggex9gxJzw2&t=6e6e42a6:9266)
    at c.RadEditor._onToolClick (ScriptResource.axd?d=wYaAc3J2NgVJCu2P39J4xyGaoOdrMcpsgItEXwZ_xZ-mxwwqth9gFwZgQmz64y0L50bOGm0jxdnTOv_b92sCumvlnrhdNCqVSpfDTXuridpdeelSxC1ktLGb8SRXNUQSfAkHpn5XxFbvggex9gxJzw2&t=6e6e42a6:8619)
    at Array.<anonymous> (ScriptResource.axd?d=drtcXVcvAjvxxGTIp4ks_jsffAtTgDZa7F-xsErOE7x83oPLnSroIDP2Rlpln027LL6pHm8wDFlVd2TfNwyX9tsTD0IfApyfv4p2GRpAUsfag9bRTF3ZhqYQPg2KFASuXMmfKVcURGhOxnF7S60OLuj9cWAWD2oOw-AOIsKJVpoN8aJcHQVfLpfuW8e9J_z70&t=74693645:47)
    at ScriptResource.axd?d=drtcXVcvAjvxxGTIp4ks_jsffAtTgDZa7F-xsErOE7x83oPLnSroIDP2Rlpln027LL6pHm8wDFlVd2TfNwyX9tsTD0IfApyfv4p2GRpAUsfag9bRTF3ZhqYQPg2KFASuXMmfKVcURGhOxnF7S60OLuj9cWAWD2oOw-AOIsKJVpoN8aJcHQVfLpfuW8e9J_z70&t=74693645:3484

Render mode configuration in the web.config

<add key="Telerik.Web.UI.RenderMode" value="Auto" />
It seems, code is looking for FindAndReplace key in this._dialogDefinitions, but it's not there. However, the key FindAndReplaceSettings is there.

Position the cursor between the words SharePoint and Whether in the first paragraph and add a line break, after that press Backspace and you'll see that the new line does not disappear.

Adding new sections between existing paragraphs or after the last paragraph seems to work fine, but if you have to break up an existing paragraph into two paragraphs and then want to turn it back into one you won't be able to.

https://www.screencast.com/t/NAniQ50c2UU9

When the Track Changes is enabled and a <p> element contains nothing but whitespace (newline, space or tab characters), any time one character is deleted, the entire element is deleted 

Another issue relating to this, is that when the line is deleted, if there is another whitespace <p> element above the element, the cursor is placed not on that line, but on whatever line is next without any whitespace. 

This behavior can be reproduced in the track-changes demo (Found at https://demos.telerik.com/aspnet-ajax/editor/examples/trackchanges/defaultcs.aspx ) ,by following these steps:

1. Create a <p> element containing some text
2. Below this element, create 3 more containing nothing but whitespace
3. On the last line enter a space and then press the backspace key

The cursor will be moved to the <p> element containing text and the entire element will be deleted (not just the space which was entered)