Created Issue: BalloonPopupExtender [27112]

BalloonPopupExtender is visible by default at first time of page load when it is inside of a tabpanel of tabcontainer.
This problem is occuring only if i place control inside tabpanel of tabcontainer..

My Code is below

<cc1:TabContainer ID="tabDemograph" runat="server">
<cc1:TabPanel ID="tabHotels" runat="server" HeaderText="Hotels" >
<ContentTemplate>

<asp:ListBox ID="lbCity" runat="server" SelectionMode="Multiple" Height="100px"
Width="141px"></asp:ListBox>
<cc1:BalloonPopupExtender ID="lbCity_BalloonPopupExtender" runat="server"
BalloonPopupControlID="Panel1" CustomCssUrl="" DynamicServicePath=""
Enabled="True" ExtenderControlID="" TargetControlID="lbCity">
</cc1:BalloonPopupExtender>
<asp:Panel ID="Panel1" runat="server">
welcome
</asp:Panel>
</ContentTemplate>
</cc1:TabPanel>
</cc1:TabContainer>