ActiveTabChanged event of ajax tab control is not firing.

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C#

ASP.NET

Javascript

Ajax

I have taken three tab. when i navigate from one tab to another, TabContainer1_ActiveTabChanged does not fire.
Following is markup code:

<asp:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server">
       </asp:ToolkitScriptManager>
       <asp:TabContainer ID="TabContainer1" runat="server" Width="600" ActiveTabIndex="0"
           OnActiveTabChanged="TabContainer1_ActiveTabChanged" AutoPostBack="true" OnClientActiveTabChanged="changeTab">
           <asp:TabPanel ID="TabPanel1" runat="server">
               <HeaderTemplate>
                   Personal Details</HeaderTemplate>
               <ContentTemplate>
                   <asp:Label ID="Label1" runat="server" Text="First Name"></asp:Label>
                   <asp:TextBox ID="txtFName" runat="server"></asp:TextBox><br />
                   <asp:Label ID="Label2" runat="server" Text="Surname"></asp:Label>
                   <asp:TextBox ID="txtLName" runat="server"></asp:TextBox><br />
                   <asp:Button ID="btnPersonal" runat="server" Text="Save" OnClick="btnPersonal_Click" /><br />
                   <asp:Label ID="lblTabId1" runat="server"></asp:Label>
               </ContentTemplate>
           </asp:TabPanel>
           <asp:TabPanel ID="TabPanel2" runat="server">
               <HeaderTemplate>
                   Educational Details
               </HeaderTemplate>
               <ContentTemplate>
                   <asp:Label ID="lblQualification" runat="server" Text="Qualification"></asp:Label>
                   <asp:TextBox ID="txtQualification" runat="server"></asp:TextBox><br />
                   <asp:Label ID="lblCollege" runat="server" Text="College"></asp:Label>
                   <asp:TextBox ID="txtCollege" runat="server"></asp:TextBox><br />
                   <asp:Button ID="btnQualification" runat="server" Text="Save" /><br />
                   <asp:Label ID="lblTabId2" runat="server"></asp:Label>
               </ContentTemplate>
           </asp:TabPanel>
           <asp:TabPanel ID="TabPanel3" runat="server">
               <HeaderTemplate>
                   Professional Details
               </HeaderTemplate>
               <ContentTemplate>
                   <asp:Label ID="lblCompany" runat="server" Text="Comapny"></asp:Label>
                   <asp:TextBox ID="txtCompany" runat="server"></asp:TextBox><br />
                   <asp:Label ID="lblLocation" runat="server" Text="Location"></asp:Label>
                   <asp:TextBox ID="txtLocation" runat="server"></asp:TextBox>
                   <br />
                   <asp:Button ID="btnProfessional" runat="server" Text="Save" /><br />
                   <asp:Label ID="lblTabId3" runat="server"></asp:Label>
               </ContentTemplate>
           </asp:TabPanel>
       </asp:TabContainer>

this is my event in .cs:

protected void TabContainer1_ActiveTabChanged(object sender, EventArgs e)
    {

        lblTabId1.Text = TabContainer1.ActiveTabIndex.ToString();
        lblTabId2.Text = TabContainer1.ActiveTabIndex.ToString();
        lblTabId3.Text = TabContainer1.ActiveTabIndex.ToString();
    }

When i navigate from one tab to another, postback(asynchronous) does not happened but when i click on save button, postback occurs and ActiveTabChanged event gets fired.
pls help me..!