AJAX :: Collapsible Panels With Extender

I have 2 collapsible panel. The first panel is expanded by default and second panel is collapsed. When I insert a user control in the first panel (about 650px height) it displays it but the content overflows into second panel header. I have autosize to none and height to 0px in the cssclass.

The content section in panel is not expanding to fit. However if any place any amount of static text it works perfectly. Also when I collapse the first panel the rest of the panel is disappearing when an user control is used. Am I missing something. The same problem when I tried to used ajax accordion

<asp:CollapsiblePanelExtender
ID="CollapsiblePanelExtender1" runat="server"
TargetControlID="PanelContentMain"
ExpandControlID="PanelTitleMain"
CollapseControlID="PanelTitleMain"
Collapsed="True"
TextLabelID=""
ExpandedText=""
CollapsedText=""
ImageControlID="Image1"
CollapsedImage="Images/accordion_active.png"
ExpandedImage="Images/accordion_active.png"
SuppressPostBack="True" >
</asp:CollapsiblePanelExtender>
<asp:CollapsiblePanelExtender
ID="CollapsiblePanelExtender2" runat="server"
TargetControlID="PanelContentAddress"
ExpandControlID="PanelTitleAddress"
CollapseControlID="PanelTitleAddress"
Collapsed="True"
TextLabelID=""
ExpandedText=""
CollapsedText=""
ImageControlID="Image1"
CollapsedImage="Images/accordion_active.png"
ExpandedImage="Images/accordion_active.png"
SuppressPostBack="True" >
</asp:CollapsiblePanelExtender>
THe header and content
----------------------------------
<asp:Panel ID="PanelTitleMain" runat="server" CssClass="collapsePanelHeader">
Application Information
</asp:Panel>
<asp:Panel ID="PanelContentMain" runat="server" CssClass="collapsePanel" >
<ucpers:ucpspers id="ucpspers1" runat="server" />
</asp:Panel>
<asp:Panel ID="PanelTitleAddress" runat="server" CssClass="collapsePanelHeader">
Contact Address Information
</asp:Panel>
<asp:Panel ID="PanelContentAddress" runat="server" CssClass="collapsePanel">
Contact Address
</asp:Panel>
The css
-------------
.collapsePanel
{
width:640px;
height:0px;
background-color:White;
overflow:hidden;
background-color: #E7FBFB;
border: 1px double #2E4d7B;
}
.collapsePanelHeader
{
width:640px;
height:20px;
color:Black;
background-color:#DDBF7D;
font-weight:bold;
font-size: 12px;
font-family:Arial,Verdana;
padding:5px;
cursor:pointer;
vertical-align:middle;
overflow:hidden;
border: 1px solid #b85dc3;
cursor: pointer;
}