AJAX :: Page.IsPostBack Returns False On Partial Page Update?

I have a page with a (gridview nested within a gridview) in an UpdatePanel (UpdateMode="Conditional"). The nested gridview drops down when you click on an arrow and then you can click on each subgrid rows command field. The gridviews are loaded from the Page_Load event. When I click on the commandfield in the subgrid the Page_Load fires during the partial page postback. From what I have read this is normal with UpdatePanels. But What I don't understand is why both Page.IsPostBack and ScriptManager.GetCurrent(Page).IsInAsyncPostBack test false after I click on the command field in my grid. I need to stop the rebinding of the gridviews ( which causes the subgrid to collapse ) when the command field is clicked.Also: I am using MasterPages and the <asp:ScriptManager ID="ScriptManager1" runat="server"> </asp:ScriptManager> is located in my mater page form section.Would anyone have any suggestions how to test if a partial page postback is occuringHere is a link to the page source: http://pastebin.org/153774here is a link to the code behind: http://pastebin.org/153781