In August 2011 Microsoft released the "Microsoft .NET Framework 4 Reliability Update 1" (http://support.microsoft.com/kb/2533523
) which amongst other things fixes two issues with the UpdatePanel control when using the new HTML5 input types such as "tel", "email" etc.
MicrosoftAjaxWebForms.js was updated as part of Reliability Update 1.
The result is that when you have an input control that uses one of the new HTML5 types e.g. <asp:TextBox ID="txtTelNo" type="tel" runat="server" /> and this is within an UpdatePanel, when you browse the page using recent versions of Chrome, Firefox or Safari (and probably other browsers) these fields do not postback.
The impact of this is that using the Toolkit prevents the HTML5 fixes in the Reliability Update 1 from working and HTML5 input controls do not work with browsers other an IE.
The sample code attached can be used to demonstrate the problem. In a brand new, empty web site project the code works with Chrome etc. but in a site that references the Toolkit, it does not.