C# - Why Page Number Is Not Enabled Correctly In Listview And Datapager

I am using listview and datapager for display. I use two level of listview, where inner listview item can be 6 types. I use my own datasource. I only need to display 1 inner listviewitem per page. It display each page correctly, but page number is not set right, eg, when 2nd page (other as well) is click, 2nd page number is not disabled while 1st page number is still disabled. Here is the code:

<div style="margin: 10px;">
<asp:ListView ID="rptExercise2" runat="server"
ItemPlaceholderID="itemPlaceHolder1" OnItemDataBound="ExerciseBound" OnPagePropertiesChanging="ChangeExercise">
<LayoutTemplate>
<asp:PlaceHolder ID="itemPlaceHolder1" runat="server" />
</LayoutTemplate>
<ItemTemplate>
<h2><asp:Label ID="lbName" runat="server" /></h2>
<asp:ListView ID="rptContent2" runat="server" ItemPlaceholderID="itemPlaceHolder2" OnItemDataBound="ContentBound">
<LayoutTemplate>
<asp:PlaceHolder ID="itemPlaceHolder2" runat="server" />
</LayoutTemplate>
<ItemTemplate>
<div style="padding: 5px;" >
<div>
<asp:Label ID="lbID" runat="server" Text='<%# Eval("ID") %>' Visible="false" />
<asp:Label ID="lbWrapper" runat="server" Text='<%# Eval("Wrapper") %>' Visible="false" />
<asp:Label ID="lbAudioQuestion" runat="server" Visible="false" />
<div style="text-align: right;"><asp:Label ID="lbAudioAnswer" runat="server" Visible="false" /></div>
<div style="text-align: right;"><asp:TextBox ID="tbAnswer" runat="server" TextMode="MultiLine" CssClass="tb" Width="50%" Height="60" Visible="false" /></div>
<div style="margin-left: 20px;"><asp:RadioButtonList ID="rblChoice" runat="server" Visible="false" /></div>....................................