Having a font/span tag with applied inline font-size style cannot be formatted by FontSize tool.  

This is a possible workaround that removes font-size inline style when size attribute is to be added:

<telerik:RadEditor runat="server" ID="RadEditor1" OnClientCommandExecuting="OnClientCommandExecuting">
    <Tools>
        <telerik:EditorToolGroup>
            <telerik:EditorTool Name="FontSize" />
        </telerik:EditorToolGroup>
    </Tools>
    <Content>
       <p><span style="font-size:15px;">text</span></p>
    </Content>
</telerik:RadEditor>

<script>
    function OnClientCommandExecuting(editor, args) {
        var command = args.get_commandName();
        if (command === "FontSize") {
            $telerik.$(editor.getSelectedElement()).css("font-size", "");
        }
    }
</script>

Communication between Style Builder and Table Wizard does not work. 

Adding the following link should not change the URL:

http://test.com?a=bc%3do

Programmatically added EditorToolGroup to the RadEditor's Ribbonbar is not displayed when the control is localized in Lightweight rendering.

Based on customer feedback:

1) Toggle full screen
2) Finish AJAX spell checker
3) Then full screen icon is not selected even the editor is in full screen mode

You can apply this CSS override to bring back the RadEditor defaults for the HTML mode. 

.RadForm .RadEditor .reTextArea {
    padding: 0;
    width: 100%;
    height: 100%;
    border:0;
    box-sizing: border-box;
    font-size: 11px;
    font-family: inherit;
}

The problem is only reproducible in Chrome. The error does not affect the content or the functionality of TrackChanges. Chrome throws this exception because it tries to select unavailable DOM range. 

The following error is thrown when RadEditor is set in Inline mode with Material skin:
TypeError: view.modesRowContainer(...) is undefined


Workaround:

Sys.Application.add_load(function () {
                var EditorLightweightView = Telerik.Web.UI.Editor.LightweightView;
                EditorLightweightView.prototype.modesRowContainerOriginal = EditorLightweightView.prototype.modesRowContainer;
                EditorLightweightView.prototype.modesRowContainer = function () {
                    return this.modesRowContainerOriginal() || {};
                }
            });

The error that is thrown is  "Unable to get property 'get_id' of undefined or null reference". 


Workaround:
  var EditorPrototype = Telerik.Web.UI.RadEditor.prototype;
            EditorPrototype.get_rippleZonesConfigurationOriginal = EditorPrototype.get_rippleZonesConfiguration;
            EditorPrototype.get_rippleZonesConfiguration = function () {
                if (!this._rippleZonesConfiguration) {
                    this._rippleZonesConfiguration = this.get_rippleZonesConfigurationOriginal();
                }
                return this._rippleZonesConfiguration;
            }

Workaround: Set Lightweight for RadMenu in web.config:

    <add key="Telerik.Web.UI.Menu.RenderMode" value="lightweight" />

When you change the render mode of RadEditor from Lightweight to Classic programmatically (like in the RenderModes demo: http://demos.telerik.com/aspnet-ajax/editor/examples/rendermodes/defaultcs.aspx), wrong items are loaded in the context menu that is displayed by right-clicking on a table cell.

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

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

http://demos.telerik.com/aspnet-ajax/editor/examples/trackchanges/defaultcs.aspx

Use the following markup:

<p><ins author="RadEditorUser" command="Insert" timestamp="1461912623680" title="Inserted by RadEditorUser on 4/29/2016, 9:50:23 AM" class="reU0">Apple</ins></p>
<p>&nbsp;</p>
<p>&nbsp;</p>
<p><ins author="RadEditorUser" command="Insert" timestamp="1461912654319" title="Inserted by RadEditorUser on 4/29/2016, 9:50:54 AM" class="reU0">Banana</ins></p>

Place the cursor in front of Banana

Press backspace

Expected: The empty paragraph is deleted OR the empty paragraph deletion is tracked (leave the preferred behavior in the comments)

Actual: The last letter of the first paragraph is deleted

The content of RadEditor overflows the height ot the content area in Mobile Safari (tested with IOS 9.3). The issue is reproducible as of version 2015.3.930

Reproduction code:
        <telerik:RadEditor ID="emailMessageInput" runat="server" Style="font-size: 12px;" Height="450" Width="600">
            <Content>
                foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />foo<br />
            </Content>
        </telerik:RadEditor>
        <br />
        <asp:Button ID="btn" runat="server" Text="the editor overflows on an ipad" />

The height is bigger than the viewport.

If there are toolbars docked at the left or right, the right toolbar is hidden due to larger width. 


You can fix a bit the width by using this code:

<telerik:RadEditor ID="RadEditor1" runat="server" RenderMode="Lightweight" OnClientCommandExecuted="OnClientCommandExecuted">
    <Tools>
        <telerik:EditorToolGroup>
            <telerik:EditorTool Name="AjaxSpellCheck" />
        </telerik:EditorToolGroup>
        <telerik:EditorToolGroup dockingzone="Left">
            <telerik:EditorTool Name="AjaxSpellCheck" />
        </telerik:EditorToolGroup>
        <telerik:EditorToolGroup dockingzone="Right">
            <telerik:EditorTool Name="ToggleScreenMode"></telerik:EditorTool>
        </telerik:EditorToolGroup>
    </Tools>
</telerik:RadEditor>

<script>
    function OnClientCommandExecuted(editor, args) {
        if (args.get_commandName() === "ToggleScreenMode" && editor.isFullScreen()) {
            var editorId = editor.get_id();
            var editorElm = editor.get_element();
            var leftToolbar = $telerik.$(editorElm).find("#" + editorId + "Left.reToolBarWrapper");
            var rightToolbar = $telerik.$(editorElm).find("#" + editorId + "Right.reToolBarWrapper");

            var widthExcess = leftToolbar.width() + rightToolbar.width();

            if (widthExcess) {
                editorElm.style.width = (parseInt(editorElm.style.width) - widthExcess) + "px";
            }
        }
    }
</script>

http://demos.telerik.com/aspnet-ajax/editor/examples/overview/defaultcs.aspx

Currently, TabStrip cannot be focused because it's missing AccessKey. All elements in the dialog should be accessible.

When an input of type text is selected user cannot change its properties from Design mode. 

Workaround: 

<telerik:RadEditor runat="server" ID="RadEditor1">
    <Content>
        <input type="text" style="width: 100px; height: 22px;" />
        <br />
        
        <textarea></textarea>
    </Content>
</telerik:RadEditor>

<script>
    Telerik.Web.UI.RadEditor.prototype.getSelectedElement = function (range) {
        var editor = this;
        var contentArea = editor.get_contentArea();
        var $ = $telerik.$;
        var $Editor = Telerik.Web.UI.Editor;
        var utils = $Editor.Utils;

        if (editor.get_renderMode() === Telerik.Web.UI.RenderMode.Mobile) {
            var highlighted = $(contentArea).find(".__reTextHighlight,.__reNodeHighlight");
            if (highlighted.length) {
                var first = highlighted.get(0);
                var last = highlighted.last().get(0);
                return first === last ? first :
                    utils.findCommonAncestor(first, last);
            }
        }

        range = range || editor.getDomRange();
        if (!range) {
            var activeElement;
            try {
                activeElement = editor.get_document().activeElement;
            } catch (ex) { return undefined; }
            return $(activeElement).is('input[type=text],input[type=password],textarea') ?
                activeElement : undefined;
        }

        var container = range.commonAncestorContainer;
        if (container === contentArea || $.contains(contentArea, container)) {
            var selectedNode = $Editor.RangeEdges.commonNode(range);
            var isTextNode = utils.isTextNode(selectedNode);

            return utils.isTextNode(selectedNode) ? selectedNode.parentNode : selectedNode;
        }
    };
</script>