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

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>

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>

A new control that would respond to dynamic or highly relational data by showing relations to nodes would be extremely useful. Two examples are linked below: http://philogb.github.io/jit/static/v20/Jit/Examples/Hypertree/example1.html and http://www.visualthesaurus.com/app/view. 

The two examples show basic nodes and the ability for the end user to move through data to focus on specific data points and the map changes to show the relations stemming from that position. 

What would be useful to include would be the ability to define the points by some sort of type, and to colorize the points and/or connectors. The Telerik Diagram and Org Charts have a very basic type of relation - but are insufficient to map to the level of the examples.

Where we would like to use this would be to map our software and services. Linking all dependencies and allowing a dynamic view of these would be extremely helpful. Our other business processes would most likely follow this example, where we could map our members to their services and costs, and rotate in on specific areas where we could focus on cost improvements.

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

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....

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

RadToolTipManager cannot find custom embedded skin, when a custom skin DLL is created with the Skins assembly builder (http://skinsassemblybuilder.telerik.com/).

Steps to reproduce:
1. Create a custom skin and wownload ZIP from Visual Style Builder (http://skinsassemblybuilder.telerik.com/)
2. Upload ZIP to Skins Assembly builder (http://skinsassemblybuilder.telerik.com/)
3. Create new project with Telerik template, turn off all options (like additional skins).
4. Add downloaded DLL as project reference.
5. Add to web.config:  <add key="Telerik.Skin" value="My_Skin" />
        <add key="Telerik.EnableEmbeddedSkins" value="true" />
        <add key="Telerik.EnableEmbeddedBaseStylesheet" value="true" />
        <add key="Telerik.Web.SkinsAssembly" value="My_Skin"/>
6. In Default.aspx, add
      <telerik:RadToolTipManager runat="server"></telerik:RadToolTipManager>

Result: an Internal Server Error is thrown:
Telerik.Web.UI.RadToolTipManager with ID='ctl03' was unable to find an embedded skin with the name 'My_Skin'. Please, make sure that the skin name is spelled correctly and that you have added a reference to the Telerik.Web.UI.Skins.dll assembly in your project. If you want to use a custom skin, set EnableEmbeddedSkins=false.

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>

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>