To get the RadWindow to center properly, you need to use its OnClientAutoSizeEnd event and  call its center() method:

This issue affects only the Q1 2016 SP1 release.

		<script>
			function OnClientAutoSizeEnd(sender, args) {
				sender.center();
			}
		</script>
		<telerik:RadWindow ID="RadWindow1" runat="server" OpenerElementID="Button1" AutoSize="true" Modal="true" OnClientAutoSizeEnd="OnClientAutoSizeEnd">
			<ContentTemplate>
				<div style="width: 600px; height: 400px; background: yellow;">dummy content for autosizing</div>
			</ContentTemplate>
		</telerik:RadWindow>
		<asp:Button ID="Button1" Text="open RW" runat="server" />

For the time being you can use the following CSS workaround:
	<telerik:RadCodeBlock ID="RadCodeBlock1" runat="server">
		<style>
		html .RadWindow_Bootstrap.rwLoading .rwExternalContent {
			background-image: url('	<%= Telerik.Web.SkinRegistrar.GetWebResourceUrl(this, typeof(RadWindow), "Telerik.Web.UI.Skins.Bootstrap.Common.loading.gif") %>')
		}
	</style>
	</telerik:RadCodeBlock>

Here is a script override that can help:

Telerik.Web.UI.Widgets.Draggable.prototype._calcConstraints = function (delta, position, constraints)
        {
            var $ = $telerik.$;
 
            var result = delta;
            //CHANGED THIS **********************************************************************************************************
            //Otherwise window can't be moved all the way to the right or bottom of screen
            //var elementWidth = this._element.offsetWidth;
            //var elementHeight = this._element.offsetHeight;
            var elementWidth = $(this._element).width();
            var elementHeight = $(this._element).height();
            //**********************************************************************************************************************
             
            if ((constraints.maxX != null && position.x + elementWidth > constraints.maxX) ||
                (constraints.minX != null && position.x < constraints.minX) ||
                (constraints.maxY != null && position.y + elementHeight > constraints.maxY) ||
                (constraints.minY != null && position.y < constraints.minY)
                )
                return { x: 0, y: 0 };
 
            if (delta.x < 0)
                result.x = constraints.minX !== null && !isNaN(constraints.minX) ?
                    Math.max(delta.x, constraints.minX - position.x) :
                    delta.x;
            else
                result.x = constraints.maxX !== null && !isNaN(constraints.maxX) ?
                    Math.min(delta.x, constraints.maxX - position.x - elementWidth) :
                    delta.x;
 
            if (delta.y < 0)
                result.y = constraints.minY !== null && !isNaN(constraints.minY) ?
                    Math.max(delta.y, constraints.minY - position.y) :
                    delta.y;
            else
                result.y = constraints.maxY !== null && !isNaN(constraints.maxY) ?
                    Math.min(delta.y, constraints.maxY - position.y - elementHeight) :
                    delta.y;
 
            return result;
        };

There are three possible workarounds until an official fix is available

- use RenderMode=Classic


- add a check for the object fields in the handler, in every handler

			function theCloseEventsHandler(sender, args) {
				var arg = args.get_argument();
				if (arg.target && arg.which) { //it is the mouse event
					arg = null;
				}
				alert(arg);
			}


- add the check by overriding the built-in function of the dialog. Place the following script at the end of the page that hosts the RadWindows:

			var oldClose = Telerik.Web.UI.RadWindow.prototype.close;
			Telerik.Web.UI.RadWindow.prototype.close = function (arguments) {
				if (arguments.target && arguments.which) { //it is the mouse event
					arguments = null;
				}
				var _oldClose = Function.createDelegate(this, oldClose);
				_oldClose(arguments);
			}

There are two possible workarounds:

- use RenderMode=Classic
- OR, add a CSS class to the dialog and a simple CSS rule to remove the built-in font icon:
			div.withCustomIcon .rwIcon:before
			{
				content: "";
			}

			<telerik:RadWindow ID="RadWindow1" runat="server" CssClass="withCustomIcon" IconUrl="~/images/icon_16x16.png" VisibleOnPageLoad="true" RenderMode="Lightweight"></telerik:RadWindow>

This causes some empty space to remain at the bottom of the dialog. Possible workarounds are:

- set the VIsibleStatusbar property of the RadWIndowManager to false, if all your RadWindows need no statusbar; or at least to the concrete instance.

- OR, use the following script that will improve hiding the status bar element and resizing the content:

oWnd = window.radopen(pageURL, winName);
//will work for classic rendermode
oWnd.set_visibleStatusbar(false);
//will work for lightweight. In classic jQuery will not throw exceptions because of the element it cannot find
$telerik.$(".rwStatusBar", oWnd.get_popupElement()).hide();
var contentElem = $telerik.$(".rwContent.rwExternalContent", oWnd.get_popupElement());
contentElem.height(contentElem.height() + 20);

I needed this event because I wanted to implement custom logic at end of animation. I am trying to auto-size the standard dialogs when animation is enabled. Right now, the code library that I submitted for auto-sizing standard dialogs works only if there is no animation. I feel providing an AnimationCompleted event on client-side would provide more power to the developer and finer control on customizing the RadWindow when its animated.

Allow adding buttons near cancel button rather than inside form. Please see attachments.

For the time being you can use the following workaround:

		<telerik:RadWindow ID="RadWindow1" runat="server" NavigateUrl="telerik_new-logo_thumb.png" VisibleOnPageLoad="true" RenderMode="Lightweight"></telerik:RadWindow>
		<script>
			var $W = Telerik.Web.UI.Window;
			$W.LightweightRenderer.prototype.createUI = function () {
				if (this.container) return;
				var wnd = this.window;
				var isRtl = wnd._isWindowRightToLeft();
				var addCssClass = Sys.UI.DomElement.addCssClass;

				var container = document.createElement("div");
				this._appendToDom(container);
				this.container = wnd._popupElement = container;
				container.id = "RadWindowWrapper_" + wnd.get_id();

				container.className = this._getSkinCssClass();
				var customCssClass = wnd.get_cssClass();
				if (customCssClass)
					addCssClass(container, customCssClass);
				if (isRtl)
					addCssClass(container, "rwRtl");
				if (!wnd._visibleTitlebar)
					addCssClass(container, "rwNoTitleBar");

				this.setShadowCssClass(wnd._enableShadow);

				container.setAttribute("unselectable", "on");

				var containerStyle = container.style;
				containerStyle.width = wnd._width;
				containerStyle.height = wnd._height;
				containerStyle.position = "absolute";

				var titlebar = this.titlebar = wnd._titlebarElement = document.createElement("div");
				titlebar.className = "rwTitleBar";
				container.appendChild(titlebar);

				var titleWrap = document.createElement("div");
				titleWrap.className = "rwTitleWrapper";
				titlebar.appendChild(titleWrap);

				titleWrap.appendChild(this.getIconNode());
				titleWrap.appendChild(this.getTitleNode());
				wnd.set_title(wnd._title);
				titleWrap.appendChild(this.getTitleCommandsContainer());

				wnd._registerTitlebarHandlers(true);
				wnd.set_iconUrl(wnd.get_iconUrl());

				var content = this.content = $get(wnd.get_id() + "_C") || this.pendingContent || document.createElement("div");
				if (content) {
					content.style.display = "none";
					content.className = "rwContent";
					this.setContent(content);
				}

				if (!wnd._dockMode) {
					var contentFrames = content.getElementsByTagName("iframe");
					//Create content IFRAME. Due to a bug in IE regarding setting the name attribute, the following ugly code needs to be used
					var frame = contentFrames.length > 0 ?
									contentFrames[0] :
									document.createElement(($telerik.isIE && !$telerik.isIE9Mode) ? "<iframe name='" + name + "'>" : "iframe");

					var name = this.window.get_name();

					frame.name = name;
					/*jshint scripturl:true*/
					frame.src = "javascript:'<html></html>';";
					frame.style.width = "100%";
					frame.style.height = "100%";
					frame.style.border = "0px"; //set to 0
					frame.frameBorder = "0";

					//Only under IE8 it is necessary to set display = "block" for the IFRAME - otherwise it will not occupy 100% of its parent element
					if ($telerik.isIE8)
						frame.style.display = "block";

					this.contentFrame = wnd._iframe = frame;

					//FIX for IFRAME overflowing outside the RadWindow under mobile device
					if (($telerik.isMobileSafari || wnd._isiPhoneiPadAppleWebkit) && !wnd._isPredefined) {
						var iframeWrapper = document.createElement('div');
						$(iframeWrapper).addClass('rwIframeWrapperIOS');
						iframeWrapper.appendChild(this.contentFrame);
						this.content.appendChild(iframeWrapper);
						//in iOS5 having a wrapper with only overflow hidden does not resolve the frame height problem
						//we need to have explicit pixel height for that wrapper as well !!!
						if (wnd._isiOS5Safari) wnd.setContentFixedHeight(wnd.get_height(), iframeWrapper);
						wnd._iframeWrapper = iframeWrapper;
					} else {
						this.content.appendChild(this.contentFrame);
					}

					Sys.UI.DomElement.addCssClass(this.content, "rwExternalContent");

					//Create a back reference to parent RadWindow
					wnd._createBackReference();
				}

				if (wnd._visibleStatusbar) {
					var statusbar = this.statusbar = document.createElement("div");
					statusbar.className = "rwStatusBar";
					container.appendChild(statusbar);

					statusbar.appendChild(this.getStatusMessageNode());
					if (wnd.isBehaviorEnabled(Telerik.Web.UI.WindowBehaviors.Resize))
						statusbar.appendChild(this.createStatusbarResizer());
				}


				wnd._addWindowToDocument();

				if (!$telerik.isTouchDevice) //fix various issues with the control when hardware acceleration is enabled with CSS
				{
					this.container.style["Transform"] = "none";
					this.container.style["BackfaceVisibility"] = "visible";
					this.container.style["webkitTransform"] = "none";
					this.container.style["webkitBackfaceVisibility"] = "visible";
					this.container.style["OTransform"] = "none";
					this.container.style["OBackfaceVisibility"] = "visible";
					this.container.style["MozTransform"] = "none";
					this.container.style["MozBackfaceVisibility"] = "visible";
					this.container.style["msTransform"] = "none";
					this.container.style["msBackfaceVisibility"] = "visible";
				}

				//Create the popup if it has not been created
				if (!wnd._popupBehavior) {
					//Set behaviors (move, resize,etc etc) - do it here, so that the IFRAME is created and can be passed to be skipped
					//should be done only once!
					wnd.set_behaviors(wnd._behaviors);
					this.popupBehavior = wnd._popupBehavior = $create(Telerik.Web.PopupBehavior, {
						'id': ((new Date() - 100) + 'PopupBehavior'),
						'parentElement': null, 'overlay': wnd._overlay, 'keepInScreenBounds': wnd._keepInScreenBounds
					}, null, null, this.container);
				}

			};
		</script>

When the Lightweight render mode is enabled and you set large text in any of the dialogs of RadWindow, part of the text appears outside of the window.

You can workaround this issue by overriding the styles of the dialogs. Below you can check a possible approach for RadAlert:
    <style type="text/css">
        div.RadWindow {
            overflow: auto;
            height: auto !important;
        }

        .rwDialogMessage {
            padding-bottom: 30px;
        }
    </style>

The following CSS will override the built-in rules to improve the icons positioning:

            div.RadWindow_Glow .rwTable .rwTitlebarControls .rwIcon
            {
                margin: 3px 5px 0 0;
            }

            div.RadWindow_Silk .rwTable .rwTitlebarControls .rwIcon
            {
                margin: 2px 5px 0 0;
            }

            div.RadWindow_Bootstrap .rwTable .rwTitlebarControls .rwIcon
            {
                margin: 6px 5px 0 0;
            }

A simple workaround is to add the needed border via CSS:

            .RadWindow.rwNoTitleBar
            {
                padding-top: 0.5em;
            }

As a workaround you can manually display the loading panel as per this KB - http://www.telerik.com/support/kb/aspnet-ajax/window/details/custom-loading-sign-for-radwindow

Move the dialog after scrolling to the bottom and its content scrolls either a bit, or to the top (depending on the used browser).
 The scroll position must be preserved and unchanged by the RadWindow control, regardless of the circumstances

There are two workarounds:
- set the EnableShadow property in the markup
- OR, for Lightweight RenderMode, add a CSS class:

<telerik:RadWindow ID="RadWindow_MyInfo" runat="server" RenderMode="Lightweight"></telerik:RadWindow>
<asp:Button ID="Button1" Text="show wnd" OnClientClick="test(); return false;" runat="server" />
<script>
	function test() {
		var myinfo = $find('<%=RadWindow_MyInfo.ClientID%>');
		myinfo.setUrl("../Dialogs/MyInfo.aspx");
		myinfo.set_enableShadow(true);
		myinfo.show();
		$telerik.$(myinfo.get_popupElement()).addClass("rwShadow");
	}
</script>

According to client reports, having an ID set to the HTML element that holds the text of the predefined dialogs improves the way JAWS handles them. Here is a small example that shows how you can do that:

<telerik:RadWindowManager ID="RadWindowManager1" runat="server" OnClientShow="OnClientShow"></telerik:RadWindowManager>
<script>
	function OnClientShow(sender, args) {
		if (sender._isPredefined) {
			var dialogId = sender.get_id();
			var textContainer = $telerik.$(".rwDialogText", sender.get_contentElement());
                        //for the Lightweight RenderMode, use the ".rwDialogMessage" selector
			var textConainerIdPrefix = "dialogContent_";
			textContainer.attr("id", textConainerIdPrefix + dialogId);
		}
	}
	function pageLoad() {
		radalert("a warning");
		radconfirm("a confirmation");
		radprompt("a prompt");
	}
</script>

At present, when a RadWindow is pinned, it still uses position: absolute and an interval is initiated to recalculate its position every 100ms. This causes it to visibly "jump" when the user scrolls the page because of the interval update in its location.

Instead, position: fixed should be used to avoid the position calculation on an interval.

The easiest workaround is to remove the overlay (e.g., set the Overlay property to false or call the set_overlay(false) client-side method). In most cases an overlay is not needed, as it is used only for showing the popup over heavyweight objects like PDFs, Flash or Java applets: http://www.telerik.com/support/kb/aspnet-ajax/window/details/control-is-shown-behind-a-heavy-weight-object-(pdf-flash-activex-etc)

You can work around this by storing the currently focused element before calling autoSize()
and then using the OnClientAutoSizeEnd event (http://www.telerik.com/help/aspnet-ajax/window-client-side-events-onclientautosizeend.html) to restore the focus.

//this goes in the content
function autoSizeWnd() {
	//code that manipulates the content so autosizing is needed
	var oWnd = getRadWindow();
	if ($telerik.isIE) { //assumes you have the Telerik core client-side libraries loaded (e.g., by having a Telerik control on this page). If you don't, you can skip the check or add them manually
		oWnd.__currActElem = document.activeElement;
	}
	oWnd.autoSize();
}


//this goes in the main page where the RadWindow is declared
function autoSizeEndHandler(sender, args) {
	setTimeout(function () {
		if (sender.__currActElem && sender.__currActElem.focus) {
			sender.__currActElem.focus();
		}
	}, 0);
}