Created Unassigned: ajaxToolkit:TabContainer [27707]

The ajaxToolkit:TabContainer always has the same active tab index after postback. This started after upgrading my ASP.NET VB.NET web forms project from VS2010 .net 3.5 to VS2013 .net4.0, and ran nuget to upgrade ajaxToolkit and jquery from 1.9.1 to 2.1.1. I really do not want to go back to VS2010. This is the only issue holding me up. Here's the minimalized code.

/// my javascript for postback

function ActiveTabChanged(sender, e) {
__doPostBack('TabContainer1', sender.get_activeTab().get_headerText());
}


/// the control - truncated here

<asp:UpdatePanel ID="upTabs" runat="server" UpdateMode="Conditional">
<Triggers><asp:AsyncPostBackTrigger ControlID="TabContainer1" EventName="ActiveTabChanged" />
</Triggers>
<ContentTemplate><ajaxToolkit:TabContainer ID="TabContainer1" runat="server" ActiveTabIndex="0" OnActiveTabChanged="ActiveTabChangedServer" AutoPostBack="false" OnClientActiveTabChanged="ActiveTabChanged" >
<ajaxToolkit:TabPanel ID="Tab2" runat="server" >
<ContentTemplate><asp:UpdatePanel ID="upUserDetails" runat="server" UpdateMode="Conditional">
<Triggers><asp:AsyncPostBackTrigger ControlID="TabContainer1" EventName="ActiveTabChanged" />
</Triggers>
<ContentTemplate>stuff here</ContentTemplate>
</asp:UpdatePanel></ContentTemplate></ajaxToolkit:TabPanel>

next panel, and so on.

/// code behind. the event for tab click

Protected Sub ActiveTabChangedServer(sender As Object, e As System.EventArgs) Handles TabContainer1.ActiveTabChanged
LoadDataForActiveTab() ' this is just the call to load the tab
End Sub