I cannot reproduce the issue
Can you post your test case?
Here is my test case
Master page:
<%@ Master Language="C#" %>
<%@ Register assembly="Ext.Net" namespace="Ext.Net" tagprefix="ext" %>
<!DOCTYPE html>
<html>
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<ext:ResourceManager runat="server" />
<ext:Panel runat="server" Title="Content" Width="300" Height="300" Layout="FitLayout">
<Content>
<asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server">
</asp:ContentPlaceHolder>
</Content>
</ext:Panel>
</form>
</body>
</html>
Content page:
<%@ Page Title="" Language="C#" MasterPageFile="~/Vlad/Site1.Master" %>
<%@ Register assembly="Ext.Net" namespace="Ext.Net" tagprefix="ext" %>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">
<ext:Portal runat="server" Border="false">
<Items>
<ext:PortalColumn
runat="server"
Cls="x-column-padding">
<Items>
<ext:Portlet ID="Portlet1" runat="server" Title="Another Panel 1" Icon="Accept" />
</Items>
</ext:PortalColumn>
<ext:PortalColumn
runat="server"
Cls="x-column-padding">
<Items>
<ext:Portlet ID="Portlet2" runat="server" Title="Panel 2" />
<ext:Portlet ID="Portlet3" runat="server" Title="Another Panel 2" />
</Items>
</ext:PortalColumn>
<ext:PortalColumn
runat="server"
Cls="x-column-padding1">
<Items>
<ext:Portlet ID="Portlet4" runat="server" Title="Panel 3" />
<ext:Portlet ID="Portlet5" runat="server" Title="Another Panel 3" />
</Items>
</ext:PortalColumn>
</Items>
</ext:Portal>
</asp:Content>