Progressbar Template Shows Up When It's Not Ne

问题:

I have an updatepanel that includes a textbox, a search button and a gridview. the gridview has some bound fields (first name and last name) and 1 templated field (a button).

The user inserts a name into the textbox, click the button named "search" and the gridview is filled with names and buttons (Each button adds a value to a list box).

There is also a progressbar which associated with that updatePanel and it shows a "loading" div when I click the "search" button.

<asp:UpdateProgress ID="UpdateProgress1" runat="server" 
        AssociatedUpdatePanelID="UpdatePanel1" DisplayAfter="0">
    <ProgressTemplate>
      <div>Loading...</div>
    </ProgressTemplate>
</asp:UpdateProgress>
<asp:UpdatePanel Id="UpdatePanel1" UpdateMode="Conditional" 
     ChildrenAsTriggers="False" runat="server">
   <Triggers>
      <asp:AsyncPostBackTrigger ControlID="SearchButton" EventName="Click" />
   </Triggers>
   <ContentTemplate>
       <asp:GridView>
          ...
       </asp:GridView>
   </ContentTemplate>
</asp:UpdatePanel>

And here is the problem - every time I click the buttons in the templated field, the loading div shows up too. These buttons don't cause partial postback, so why does the loading div show up?

Thanks!