CollapsiblePanelExtender在初始页面加载时不会一直打开

<asp:Panel ID="Panel1" runat="server" CssClass="panel">
    <h3>Panel 1</h3>
    <p>This is the content of Panel 1.</p>
</asp:Panel>

<asp:Panel ID="Panel2" runat="server" CssClass="panel">
    <h3>Panel 2</h3>
    <p>This is the content of Panel 2.</p>
</asp:Panel>

<ajaxToolkit:CollapsiblePanelExtender ID="CollapsiblePanelExtender1" runat="server" TargetControlID="Panel1" CollapseControlID="Panel2" Collapsed="false" ExpandControlID="Panel2" CollapsedSize="0" ExpandedSize="100" AutoCollapse="false" SuppressPostBack="true" />

var collapsiblePanelExtender = $find('<%= CollapsiblePanelExtender1.ClientID %>');
collapsiblePanelExtender._doOpen();