This causes also to cancel submit and produce an incorrect behavior.

You can use RadButton as a toggle button with type Checkbox as alternative solution:

<telerik:RadButton runat="server" ButtonType="ToggleButton" ToggleType="CheckBox" RenderMode="Lightweight" AutoPostBack="false"></telerik:RadButton>

Markup to reproduce the issue:

<telerik:RadEditor ID="RadEditor1" runat="server" EditModes="Design" RenderMode="Lightweight">
<Tools>
<telerik:EditorToolGroup>
<telerik:EditorTool Name="Bold" />
<telerik:EditorTool Name="Italic" />
<telerik:EditorTool Name="Underline" />
</telerik:EditorToolGroup>
</Tools>
<Content>
<p>test</p>
<p>test</p>
</Content>
</telerik:RadEditor>

Resolution:

<script type="text/javascript">
	(function ($UI) {
		$UI.SizerLightweight.prototype._calcUiHeight = function () {
			var that = this,
				view = that._view,
				editor = that.editor,
				calculator = new $UI.DimensionsCalculator(editor),
				toolBarContainer = view.toolBarContainer(),
				toolBarHeight = that._getComponentHeight(toolBarContainer),
				paddings = calculator.getComputedSizes(editor.get_element(), ["padding-top", "padding-bottom"]),
				margins = calculator.getComputedSizes(toolBarContainer, ["margin-bottom"]),
				borders = calculator.getComputedSizes(view.contentAreaContainer(), ["border-top-width", "border-bottom-width"]),
				modesHeight = that._getComponentHeight(view.modesRowContainer()),
				modulesHeight = that._getComponentHeight(view.modulesContainer());

			return toolBarHeight + modesHeight + modulesHeight + margins + borders + paddings;
		}
	})(Telerik.Web.UI.Editor.UI);
</script>

Please could you make a RadToggleSwitch for ASP.NET AJAX? (Similar to the WinForms control)

an email text control.
a control like a text box but that filters out the invalid characters that cannot be used in an email address. This control could be separated in 3 parts:

part1@part2.part3

When the user hits the dot "." just before part3, a autocomplete feature can make it easier (faster) to select a frequently used prefex (like .com, .net, .org, etc...). This feature can be customized by the developer. The developer can turn it on or off. He can also make an own autocomplete list and eventually restrict to a list of suffixes.
Also when you want the user to type in an email address with a fix part 2 and part 3, the developer could customize it like this (e.g. when you want the user to enter only email addresses of @gmail.com, the developer can do this by design.

The three parts in the email address are required in order to have a valid email address.

As an extra feature the control can have a "IsValid()"-method that can be used by the developer to quickly check whether the email address is valid.

Server-side as well as client-side API make sense....

RadScheduler Server-side PDF Export does not support Lightweight render mode, as specified in the respective help article:
http://docs.telerik.com/devtools/aspnet-ajax/controls/scheduler/export/pdf/overview.html

The following code snippet can be used to prevent this behavior:

<telerik:RadEditor ID="RadEditor1" runat="server">
</telerik:RadEditor>
 
<script type="text/javascript">
    (function (Editor) {
        var setCursor = Editor.Selection.prototype._setCursor;
        if (setCursor) {
            Editor.Selection.prototype._setCursor = function (node, range) {
                return Editor.Utils.isTag(node, "img") ?
                    this._setCursorAfterNode(node, range) : setCursor.call(this, node, range);
            };
        }
    })(Telerik.Web.UI.Editor);
</script>

When the user types !, #, $, % or &, the inserted character is not tracked. These characters are typed by Shift+1, Shift+3, Shift+4, Shift+5, Shift+7 keys.

Here is a workaround:
<telerik:RadEditor ID="RadEditor1" runat="server" EnableTrackChanges="true">
	<Content>
		<p>test1</p>
		<p>test2</p>
	</Content>
</telerik:RadEditor>

<script>
	(function () {
		var shouldIgnoreKey = Telerik.Web.UI.RadEditor.prototype._shouldIgnoreKey;
		Telerik.Web.UI.RadEditor.prototype._shouldIgnoreKey = function (e) {
			if (e.shiftKey) {
				if ("code" in e && /^Digit/.test(e.code)) {
					return false;
				}
				if ("key" in e && /^Digit|!|#|\$|%|&/.test(e.key)) {
					return false;
				}
				if (Telerik.Web.Browser.ie && e.keyCode >= 33 && e.keyCode <= 40) {//Shift+1, Shift+3, Shift+4, Shift+5, Shift+7, ...
					return false;
				}
			}
			return shouldIgnoreKey.call(this, e);
		}
	})();
</script>

As a workaround you can either use Lightweight render mode or Server group load mode.

When the labels' template is not defined, there is an explicit serialization like:

template:"#= dataItem.<data_bound_property> #"

which is in a collision with the DataFormatString property.

Sample code:

ASPX:
<telerik:RadHtmlChart runat="server" ID="Chart">
<PlotArea>
    <Series>
        <telerik:ColumnSeries DataFieldY="Total" Name="Total">
            <LabelsAppearance DataField="Total" DataFormatString="$#,##0.00">
            </LabelsAppearance>
        </telerik:ColumnSeries>
    </Series>
</PlotArea>
</telerik:RadHtmlChart>

C#:
protected void Page_Load(object sender, EventArgs e)
{
    Chart.DataSource = GetData();
    Chart.DataBind();
}

    
private DataTable GetData()
{
    DataTable table = new DataTable();
    table.Columns.Add(new DataColumn("Total", typeof(long)));
    table.Rows.Add(new object[] { 10000000 });
    table.Rows.Add(new object[] { 10000000 });
    table.Rows.Add(new object[] { 10000000 });
    return table;
}

The workaround is to set the ClientTemplate and remove the DataFormatString property or override the template on the client-side:

        <script type="text/javascript">
            function pageLoad() {
                var chart = $find("Chart");
                var widget = chart.get_kendoWidget();

                widget.options.series[0].labels.template = null;

                chart.repaint();
            }
        </script>

Drag and drop functionality works great. But when i drag and drop email from outlook into kendo upload control, it was unable to read it. Any solution? appreciate your help. 

Thanks,
Sundeep.

The workaround is to use the RadEditor's tab functionality instead of browser's.

<telerik:RadEditor ID="RadEditor1" runat="server" OnClientLoad="OnClientLoad">
    <Content>
        <p>test</p>
        <p>test</p>
    </Content>
</telerik:RadEditor>

<script>
    function OnClientLoad(editor, args) {
        var shortcutManager = editor.get_shortCutManager();
        if (shortcutManager.findShortCutByName("InsertTabMozilla")) {
            shortcutManager.removeShortCut("InsertTabMozilla");
            editor.addShortCut("InsertTab", "TAB");
        }
    }
</script>