Cookie law loads a <form> tag before the <form> tag of the framework, hence the dropdown is placed in the hidden cookie form instead of the correct one.

REPRO

    Run the snippet below
    Inspect the DOM (at the beginning of the form you will see the .rtbSlide element)
    Click the toolbar button to invoke an ajax request

actual: the .rtbSlide element is multiplied with every request

expected: the toolbar is fully disposed

        <asp:UpdatePanel runat="server">
            <ContentTemplate>
                <telerik:RadToolBar RenderMode="Lightweight" ID="RadToolBar1" runat="server"
                    AutoPostBack="true">
                    <Items>
                        <telerik:RadToolBarButton Text="postback to test">
                        </telerik:RadToolBarButton>
                    </Items>
                </telerik:RadToolBar>
            </ContentTemplate>
        </asp:UpdatePanel>


WORKAROUND

        <script>
            var oldDispose = Telerik.Web.UI.RadToolBar.prototype.dispose;
            Telerik.Web.UI.RadToolBar.prototype.dispose = function()
            {
                if (this._moreButtonDropDown && typeof this._moreButtonDropDown.dispose == 'function') {
                    this._moreButtonDropDown.dispose();
                }
                oldDispose.call(this);
            }
        </script>

In order to prevent clicking on the same button twice, when server-side click button is handled, the RadToolBar should be disabled or the clicked button. For that reason we are going to expose the following property:
SingleClick = None/Button/ToolBar.

In case that you want SingleClick property on RadToolBarButton, please leave us a comment with your feedback.

The disable buttons of RadToolbar do not appear as disabled under in IE7, IE8, and Chrome.