For the time being the following workaround can be used:

ASPX:

       <telerik:RadButton ID="RadButton1" runat="server" Text="Click" NavigateUrl="http://www.google.bg" Target="_blank" ButtonType="LinkButton">
        </telerik:RadButton>
        <script>
            Telerik.Web.UI.Button.NavigationFunctionality.prototype._handleNavigateUrl = function () {
                $ = $telerik.$;
                var that = this,
                    target = that.options.navigateTarget,
                    url = that.options.navigateUrl;

                if (target && target == "_blank")
                    window.open(url);
                if (target && target == "_parent")
                    window.parent.location.href = url;
                if (target && target == "_top")
                    window.parent.location.href = url;
                else if (!target || target == "_self")
                    window.location.href = url;
                else {
                    var targetFrame = $("iframe[name='" + target + "']").get(0)
                                        || $("frame[name='" + target + "']").get(0)
                                        || $("#" + target).get(0);

                    if (targetFrame && targetFrame.tagName.toLowerCase().indexOf("frame") > -1)
                        targetFrame.setAttribute("src", url);
                }
            }
        </script>

Declined with the reason:

Item is a duplicate of http://feedback.telerik.com/Project/108/Feedback/Details/127356

 Currently the value of RadButton's property 'Width' is not applied correctly and its width is not as specified.

A workaround is using ButtonType=SkinnedButton or using the Glow or BlackMetroTouch skin.
You can use the following CSS workaround to remove the additional opacity Safari adds for the input that results in the sprite being visible:
        .rbDisabled .rbDecorated {
            opacity: 1;
        }

For the time being the following workaround can be used:

CSS:

    <style>
     .RadButton.RadButton_Metro.rbSkinnedButton:focus input.rbDecorated {
            background-color: #25A0DA !important;
        }
    </style>

        <telerik:RadSkinManager ID="RadSkinManager1" runat="server" Skin="Metro"></telerik:RadSkinManager>
        <telerik:RadTextBox ID="RadTextBox1" runat="server"></telerik:RadTextBox>
        <telerik:RadButton ID="RadButton1" runat="server" Text="click" />

For the time being the following CSS workaround can be used:

CSS:

    <style>
        html .RadButton.RadButton_Glow.RadButton.rbDisabled,
        html .RadButton.RadButton_Glow.RadButton.rbDisabled:hover,
        html .RadButton.RadButton_Glow.RadButton.rbDisabled:active,
        html .RadButton.RadButton_Glow.RadButton.rbDisabled:focus,
        html .RadButton.RadButton_Silk.RadButton.rbDisabled,
        html .RadButton.RadButton_Silk.RadButton.rbDisabled:hover,
        html .RadButton.RadButton_Silk.RadButton.rbDisabled:active,
        html .RadButton.RadButton_Silk.RadButton.rbDisabled:focus,
        html .RadButton.RadButton_Metro.RadButton.rbDisabled,
        html .RadButton.RadButton_Metro.RadButton.rbDisabled:hover,
        html .RadButton.RadButton_Metro.RadButton.rbDisabled:active,
        html .RadButton.RadButton_Metro.RadButton.rbDisabled:focus {
            background-color: transparent;
            background-image: none;
            border: none;
            box-shadow: none;
        }
    </style>

ASPX:

        <telerik:RadSkinManager ID="RadSkinManager1" runat="server" ShowChooser="true" Skin="Glow"></telerik:RadSkinManager>
        <telerik:RadButton ID="RadButton1" runat="server" ToggleType="Radio" ButtonType="ToggleButton" Checked="true" Enabled="true" />
        <telerik:RadButton ID="RadButton2" runat="server" ToggleType="Radio" ButtonType="ToggleButton" Checked="true" Enabled="false" />
        <telerik:RadButton ID="RadButton3" runat="server" ToggleType="Radio" ButtonType="ToggleButton" Checked="false" Enabled="true" />
        <telerik:RadButton ID="RadButton4" runat="server" ToggleType="Radio" ButtonType="ToggleButton" Checked="false" Enabled="false" />

The width of the RadButton is higher than the actual one with Silk and Glow skins.

        <telerik:RadButton ID="RadButton1" runat="server" Skin="Silk" Width="300px"></telerik:RadButton>
        <br />
        <telerik:RadButton ID="RadButton2" runat="server" Skin="Glow" Width="300px"></telerik:RadButton>
        <br />
        <telerik:RadButton ID="RadButton3" runat="server" Skin="Default" Width="300px"></telerik:RadButton>
        <br />

Resolution:

    <style>
        span.RadButton {
            -moz-box-sizing: border-box;
            box-sizing: border-box;
        }
    </style>

For the time being the following CSS workaround can be used:

CSS:

        <style>
            .RadButton.RadButton_Glow.rbSkinnedButton {
                vertical-align: top;
            }
        </style>
Where Glow is the name of the skin that has larger dimensions (e.g., Silk, Glow, etc).
ASPX:

       <telerik:RadSkinManager ID="RadSkinManager1" runat="server" ShowChooser="true" Skin="Glow"></telerik:RadSkinManager>
        <telerik:RadTextBox runat="server" ID="txtAdminUser" />
        <telerik:RadButton runat="server" ID="btn1" Text="Add" ButtonType="StandardButton" />

Currently RadButton configured as a toggle radio/checkbox button doesn't accept custom icons to be used because it already has predefined icons. For the time being the ButtonType property can be set to "StandardButton" and its background image can be hidden. For example:
CSS:
<style>
    .RadButton_Default.rbSkinnedButton,
    .RadButton_Default .rbDecorated,
    .RadButton_Default.rbVerticalButton,
    .RadButton_Default.rbVerticalButton .rbDecorated,
    .RadButton_Default .rbSplitRight,
    .RadButton_Default .rbSplitLeft {
        background-image: none !important;
    }
</style>
ASPX:
<telerik:RadButton ID="RadButton3" runat="server" GroupName="OverSampling"
    Text="" ButtonType="StandardButton" ToggleType="Radio" Checked="false" AutoPostBack="false">
    <ToggleStates>
        <telerik:RadButtonToggleState Text="Yes" PrimaryIconUrl="radio6-on.png" Selected="true" />
        <telerik:RadButtonToggleState Text="Yes" PrimaryIconUrl="radio6-off.png" />
    </ToggleStates>
</telerik:RadButton>
 
<telerik:RadButton ID="RadButton4" runat="server" GroupName="OverSampling"
    Text="No" ButtonType="StandardButton" ToggleType="Radio" AutoPostBack="false" Checked="true">
    <ToggleStates>
        <telerik:RadButtonToggleState PrimaryIconUrl="radio6-on.png" Selected="true" />
        <telerik:RadButtonToggleState PrimaryIconUrl="radio6-off.png" />
    </ToggleStates>
</telerik:RadButton>

The workaround is to override the background image of the button:

CSS:

    <style>
        .RadButton.RadButton_Default.rbLinkButton .rbPrimaryIcon {
            background-image: url("images/Groups (16x16).png");
        }
    </style>

ASPX:

       <telerik:RadButton ID="RadButton1" runat="server" ButtonType="LinkButton" Text="Click" Skin="Default">
            <Icon PrimaryIconUrl="images/myImage (16x16).png" PrimaryIconTop="2" PrimaryIconLeft="2" />
        </telerik:RadButton>

Currently disabled RadButton doesn't have a border for Silk skin. For the time being the border can be set manually:

        <telerik:RadButton ID="RadButton1" runat="server" Skin="Silk" Text="Submit" BorderColor="#C9C9C9" BorderWidth="1px" Enabled="false">
        </telerik:RadButton>

Currently when cookiless session is enabled and RadButton with custom image is used the Image is not displayed, until the button is hovered.

ASPX:

        <telerik:RadButton ID="ButtunTest" runat="server" Icon-PrimaryIconUrl="~/Examples7/eClose.png" Text="Testbutton"
            Width="200px" UseSubmitBehavior="False" />

Web.Config:

  <system.web>
        <sessionState cookieless="true"></sessionState>
  </system.web>

The workaround is to override the background image of the button:

    <style>
        .RadButton.RadButton_Default.rbSkinnedButton .rbPrimaryIcon {
            background-image: url("/RadControlsWebSite2/Examples7/eClose.png");
        }
    </style>

If the Width property of a RadButton is set, its appearance in the Visual Studio 2012 Design view will be broken.

The icons sprite starts showing when the width is sufficiently large, test with different values, e.g. 80px, 100px, 200px, 400px, etc.

RadButton peforms a duplicate request (the second request aborts the first one) when the following conditions are met:

-The page is opened from Visual Studio 2008

- A RadButton exists on the page and the form is submitted when a text box is focused and enter key is hit.

-Default button is not set to the form.

-RadButton's UseSubmitBehavior is set to true

-.NET Framework 3.5 is used.

-The browser is Internet Explorer.

The workaround is to either set Default button for the form or set the UseSubmitBehavior property of the RadButton to false.

Currently when the RadButton is clicked and a modal RadWindow that contains another button is opened and then the second button is clicked with enter key, so that it closes the RadWindow, the first RadButton is clicked again. The workaround is to set the Modal property of the RadWindow to false.

Currently when the RadButton is focused and the Enter key is pressed, the server-side event OnClick is not triggered. When the Enter key is pressed again, the server-side event is executed.

The issue is reproduced when a dialog is opened in OnClientClicking event.

The workaround is to use

-Either the OnClientClicked event
-OR trigger the server click of the RadButton in the OnClientClicking event:
		<script type="text/javascript">
			function OnClientClicking1(sender, args) {

				alert("Client-click triggered");
				sender.click();
			}
		</script>

When a RadButton with a PostBackUrl property set is located inside an UpdatePanel,  it does not redirect to the PostBackUrl on click and a JavaScript error message is thrown.

The workaround is to use:

- Either a RadButton (ButtonType="LinkButton") and set its NavigateUrl to the desired page that is to be redirected
   
-OR a RadButton (ButtonType="StandardButton") and use its OnClientClicking event handler to cancel the postback and redirect to the desired page through window.location.href. For example:

    <script type="text/javascript">
        function OnClientClicking(sender, args) {

            window.location.href = "http://www.bing.com";
            args.set_cancel(true);

        }
    </script>