You can configure the confirm dialog through a ConfirmText property that defines the confirmation text. The boolean result can be exposed in the arguments of the click event. If there is a RadWindowManager on the same page a radconfirm should be used otherwise - the browser one.

For the time being the functionality can be achieved manually as illustrated in this demo - http://demos.telerik.com/aspnet-ajax/button/examples/confirm/defaultcs.aspx

When a RadButton with configured ValidationGroup is used on a master page its server-side event 'Click' is not raised in:
-Internet Explorer and Chrome, but FireFox and Opera.
-In all browsers when the master page contains a RadAjaxManager.

When a RadButton is clicked and the following conditions are met:
    -Page validation is not passed
    -Button's postback is cancelled in OnClientClicking event by setting args.set_cancel(true)
the postback of other RadButtons will not be performed.

Reproduced with latest official (2016.1.113) and internal (2016.2.128) in all browsers. Not reproducible with 2015 Q3 SP1.

Code to reproduce the problem:

    <asp:Button runat="server" ID="GoStep2" OnClick="GoStep2_Click" Text="Next" />
            <asp:Panel runat="server" ID="Panel1">
                <asp:Button Text="aspButton" runat="server" />
                <telerik:RadButton ID="Button1" Text="radButton" runat="server" />
            </asp:Panel>
 protected void Page_Load(object sender, EventArgs e)
    {
        Panel1.Enabled = false;
    }
 protected void GoStep2_Click(object sender, EventArgs e)
    {
        Panel1.Enabled = true;
    }


1 click the Next  button

3. When the page loads after the postback the RadButton remains disabled, unlike the asp:Button. 

Code that reproduces the issue:

        <asp:TextBox ID="Textbox1" runat="server" ValidationGroup="vg1" />
        <telerik:RadButton ID="RadButton1" runat="server" ValidationGroup="vg1" Text="click" />
        <asp:RequiredFieldValidator ID="Requiredfieldvalidator1" ErrorMessage="text box is empty" ControlToValidate="Textbox1" ValidationGroup="vg1" runat="server" />
        <asp:ValidationSummary ID="Validationsummary1" runat="server" ValidationGroup="vg1" ShowMessageBox="true" />

Common scenario is to use PrimaryIconCssClass and SecondaryIconCssClass to decorate custom icons. Common situation is using bootstrap's classes for the glyphicons.

In order to workaround this you can use custom CSS rules and define the expected content properties for the before elements. This is an example with bootstrap icons (http://glyphicons.bootstrapcheatsheets.com/). 


<style>
    .rbPrimaryIcon.glyphicon-filter:before,
    .rbSecondaryIcon.glyphicon-filter:before {
        content: "\e138";
    }
</style>

<telerik:RadButton ID="RadButton2" runat="server" 
    Text="Filter" ButtonType="SkinnedButton" 
    Icon-PrimaryIconCssClass="glyphicon glyphicon-filter" >
</telerik:RadButton>

Currently when the RadButton is used as an Image button:

- There is a flickering on mouse over and mouse out.

- During the postback the image of the current or other image buttons disappears on mouse over/mouse out.

The unexpected behavior is observed under Chrome and page is hosted on Cassini. It is caused due to the image requests that Chrome does for each state of the RadButton - normal and hovered.

When the PrimaryIconUrl and PrimaryHoveredIconUrl properties of the RadButton are set and a dialog is opened when OnClientClicked event is triggered, the button's icon from the hovered image persists. This behavior is observed only in FireFox.

RadButton peforms duplicate requests when:

- A RadButton exists on the page and the form is submitted when a text box is focused and enter key is hit.
- the defaultbutton property of the form is set to the id of the RadButton

For the time being the following functions' override can be used:

        <script type="text/javascript">
            Telerik.Web.UI.RadButton.prototype._isButtonActiveElement = function (eventTarget) {
                var doc = eventTarget && eventTarget.ownerDocument ? eventTarget.ownerDocument : document;
                var activeElement = doc.activeElement;
                if (!activeElement)
                    return false;
                if (activeElement === this.get_element() || $telerik.$.contains(this.get_element(), activeElement))
                    return true;
                return false;
            }

            var originalMouseClickHandler = Telerik.Web.UI.RadButton.prototype._mouseClickHandler;
            Telerik.Web.UI.RadButton.prototype._mouseClickHandler = function (args) {
                if (!this.get_enabled() || this.get_readOnly()) {
                    $telerik.cancelRawEvent(args.rawEvent);
                    return false;
                }

                var eventTarget = args.target ? args.target : args.srcElement;
                if (eventTarget === this.get_element() && !this._isButtonActiveElement(eventTarget) && !$telerik.isTouchDevice) {
                    $telerik.cancelRawEvent(args.rawEvent);
                    this.focus();
                    return false;
                }
                originalMouseClickHandler.call(this, args);
            }
        </script>

The workaround must be placed after the declaration of the RadButton, in order to take effect.

In Q3 2013 the clicking of RadButton is not raised when Enter key is pressed inside a password TextBox and the RadButton is set to be the default button for the form.

The workaround is to put the following JavaScript code below the declaration of the RadButton:

                                        <script type="text/javascript">
                                            Telerik.Web.UI.RadButton.prototype._isInputTypeText = function (element) {
                                                var nodeName = element.nodeName,
                                                  type = element.type;
                                                if (nodeName != "INPUT" || !type) return false;
                                                return type == "text" || type == "password" || type == "email" || type == "number" || type == "url" || type == "search" || type == "tel";
                                            }
                                        </script>

SharePoint 2013 applies global styles to the inputs that affect the appearance of the RadButtons.For the time being the styles that SharePoints sets to the inputs can be overriden:

ASPX:
<telerik:RadButton ID="RadButton1" runat="server" Text="RadButton"><Icon PrimaryIconCssClass="rbAdd" /></telerik:RadButton>

CSS:
<style type="text/css">
    .RadButton.RadButton_Default.rbSkinnedButton input {
        padding: 0px 10px 0px 25px;
        border: none;
        margin-left: 0px;
    }
</style>

Workaraounds:
- Use the Lightweight RenderMode
- OR, use the RadCheckBox control instead

Steps to reproduce:

			<telerik:RadSkinManager runat="server" ID="rsm1" ShowChooser="true"></telerik:RadSkinManager>
			<telerik:RadButton ID="rbFileLink" runat="server" ToggleType="CheckBox" ButtonType="ToggleButton"
							   Checked="true" AutoPostBack="false">
			</telerik:RadButton>

When there is a RadButton with configured ValidationGroup, the client-side ASP.NET validation on the page will not be executed, if there are validation controls, which use the same ValidationGroup. The unexpected behaviour is observed in FireFox and Opera.

When the RadButton is used as a toggle button and some of its toggle state buttons are set with PrimaryIconCssClass property the icons might not be displayed if the following conditions are met at the same time:

-AutoPostBack property of the RadButton is set to false

-One of the togglestate buttons is selected and its PrimaryIconCssClass property is not set.

The issue does not affect the functionality of the button, just the displaying of the icons in the togglestate buttons.

When the RadButton is hovered with the mouse pointer being over the button's text, the hover state is lost. This behavior is observed with Silk and Glow skins under IE 9 or less.

The workaround is to set the ButtonType to "SkinnedButton" or "LinkButton".

When RadButton is set as default button the client side cancel event is not working when pressing Enter key.