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>

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" />

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.

Workaround: Set Lightweight for RadMenu in web.config:

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

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;
            }

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 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. 

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;
}

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

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

Communication between Style Builder and Table Wizard does not work. 

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>

Having multiple paragraphs that are formatted with color and font-size as inline styles, selecting them and applied font-size by using RealFontSize tool causes these issues:

1. Only first paragraph is properly decorated;
2. Second paragraph is stripped from any inline styles at all;
3. The next paragraphs stay without any changes applied.


Possible workaround is to disable the ConvertFontToSpan filter:

RadEditor1.DisableFilter(EditorFilters.ConvertFontToSpan);

Currentluy, any content with Asian characters is not tracked.

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


Paste some content in the Editor
Expected: The pasted content is displayed and tracked

Actual: Nothing is pasted

Workaround:
<telerik:RadEditor ID="RadEditor1" runat="server" EnableTrackChanges="true">
	<Content>
		<p>test</p>
		<p>test</p>
	</Content>
</telerik:RadEditor>

<script type="text/javascript">
	if (Telerik.Web.Browser.edge) {
		var editorPrototype = Telerik.Web.UI.RadEditor.prototype;
		var origKeydownHandler = editorPrototype._onKeyDown;
		editorPrototype._onKeyDown = function (ev) {
			var shortCut = this.get_shortCutManager().isShortCutHit(ev);
			if (!shortCut || shortCut.get_name() != "Paste") {
				origKeydownHandler.call(this, ev);
			}
		}
	}
</script>

Having some text and input inside: Highlight it in order to copy and paste leads and the content area will scroll to the top of the content area. Also, you cannot highlight the input in order to copy and paste it. 

The formatting of nested lists is lost when pasting from Word in IE10. The issue is reproducible also in IE8 and I9.

When using Table Wizard to insert a new table inside a table cell, the selected table is replaced by the one created from Table Wizard. 

Currently, the workaround is to use the plain InsertTable tool in order to nest tables.