page post back when i use ToolkitScriptManager On MasterPage does not work just for part of page
<p>in the master page i was using ScriptManager so in the content page according to below markup i had post back just for part of page.</p>

<pre><code>&lt;asp:UpdatePanel ID="UpdatePanel1" runat="server"&gt;
 &lt;ContentTemplate&gt;
 &lt;asp:DropDownList ID="ddlProjectDocument" runat="server" Height="16px" AppendDataBoundItems="True"  
     Width="212px" onselectedindexchanged="ddlProjectDocument_SelectedIndexChanged" 
    AutoPostBack="True" onload="ddlProjectDocument_Load" 
    style="font-family: 'Courier New', Courier, monospace" &gt;

    &lt;asp:ListItem Selected="True" Value="0"&gt;(select a value)&lt;/asp:ListItem&gt;
&lt;/asp:DropDownList&gt;
&lt;br /&gt;



&lt;/ContentTemplate&gt;
&lt;Triggers&gt;
&lt;asp:PostBackTrigger ControlID="ddlProjectDocument"  /&gt;


&lt;/Triggers&gt;
&lt;/asp:UpdatePanel&gt;
</code></pre>

<p>now i have added combo box to my content page so i remove ScriptManager and place ToolkitScriptManager on Master Page according to below markup for master page, now when i use drop down list control post back happen for complete page not just part like before, how i can solve this problem?</p>

<pre><code>&lt;html xmlns="http://www.w3.org/1999/xhtml"&gt;
&lt;head runat="server"&gt;
&lt;title&gt;Untitled Page&lt;/title&gt;
&lt;asp:ContentPlaceHolder id="head" runat="server"&gt;
&lt;/asp:ContentPlaceHolder&gt;
&lt;style type="text/css"&gt;
    .style1
    {
        width: 40%;
        font-size:large;
    }
&lt;/style&gt;
&lt;link href="StyleSheet.css" rel="stylesheet" type="text/css" /&gt;
 &lt;/head&gt;
 &lt;body&gt;
&lt;form id="form1" runat="server"&gt;


    &lt;ajaxtoolkit:toolkitscriptmanager ID="ToolkitScriptManager1" runat="server"&gt;
    &lt;/ajaxtoolkit:toolkitscriptmanager&gt;
</code></pre>

<p>markup of new content page is like below:</p>

<pre><code> &lt;asp:UpdatePanel ID="UpdatePanel1" runat="server"&gt;
  &lt;ContentTemplate&gt;
 &lt;asp:DropDownList ID="ddlProjectDocument" runat="server" Height="16px" AppendDataBoundItems="True"  
     Width="212px" onselectedindexchanged="ddlProjectDocument_SelectedIndexChanged" 
    AutoPostBack="True" onload="ddlProjectDocument_Load" 
    style="font-family: 'Courier New', Courier, monospace" &gt;

    &lt;asp:ListItem Selected="True" Value="0"&gt;(select a value)&lt;/asp:ListItem&gt;
&lt;/asp:DropDownList&gt;
&lt;br /&gt;

&lt;ajaxtoolkit:ComboBox ID="ComboBox1" runat="server" onload="ComboBox1_Load" 
     AutoCompleteMode="Suggest" 
     style="font-family: 'Courier New', Courier, monospace" &gt;

&lt;/ajaxtoolkit:ComboBox&gt;



&lt;/ContentTemplate&gt;
&lt;Triggers&gt;
&lt;asp:PostBackTrigger ControlID="ddlProjectDocument"  /&gt;


&lt;/Triggers&gt;
&lt;/asp:UpdatePanel&gt;
</code></pre>
