Started having this problem after the upgrade to 4.1. I have a dropdown inside of a control that is part of a Button / Menu. When you click the Button / Menu, the combo shows up but when you click it to start typing it disappears. The same combo box outside of the context of a user control works fine.

User Control
<%@ Control Language="vb" AutoEventWireup="false" CodeBehind="QSearch.ascx.vb" Inherits="Adhesion.Web.QSearch" %>

<ext2:ComboBox 
    ID="Results" 
    runat="server" 
    ValueField="Key"
    TypeAhead="false" 
    LoadingText="Searching..."
    HideTrigger="true" 
    EmptyText="Type to Search" 
    QueryDelay="1500" 
    QueryCaching="false"
    MinChars="1" 
    Border="false"
    Width="920" 
    Height="38">
 </ext2:ComboBox>
Main Page
<%@ Page Language="vb" %>
<%@ Register TagPrefix="uc" TagName="QuickSearch" Src="QSearch.ascx" %>

 <script runat="server">

     Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
     End Sub

</script>

<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <title>Simple Combo</title>
    <script type="text/javascript">
    </script>
</head>
<body>
 
    <ext2:ResourceManager ID="ResourceManager" runat="server" />

    <ext2:Window ID="Window1" runat="server" Visible="true" Maximized="true" Padding="5" Resizable="true" MinHeight="700" MinWidth="500" Closable="false">
        <TopBar>
            <ext2:Toolbar ID="Toolbar1" runat="server">
                <Items>

                    <ext2:Button ID="QuickLaunchReport" runat="server" Text="This does not work" >
                        <Menu>
                            <ext2:Menu ID="QuickLaunchReportMenu" runat="server" RenderToForm="true" Width="450" ShowSeparator="false">
                                <Items>
                                    <ext2:Panel runat="server">
                                        <Content>
                                            <uc:QuickSearch ID="QuickSearch" runat="server" />
                                        </Content>
                                    </ext2:Panel>
                                </Items>
                            </ext2:Menu>
                        </Menu>
                    </ext2:Button>

                    <ext2:Button ID="Button1" runat="server" Text="This works"  >
                        <Menu>
                            <ext2:Menu ID="Menu1" runat="server" RenderToForm="true" Width="450" ShowSeparator="false">
                                <Items>
                                    <ext2:Panel runat="server">
                                        <Items>
                                            <ext2:ComboBox 
                                                ID="works" 
                                                runat="server" 
                                                ValueField="Key"
                                                TypeAhead="false" 
                                                LoadingText="Searching..."
                                                HideTrigger="true" 
                                                EmptyText="Type to Search" 
                                                QueryDelay="1500" 
                                                QueryCaching="false"
                                                MinChars="1" 
                                                Border="false"
                                                Width="920" 
                                                Height="38">
                                            </ext2:ComboBox>
                                        </Items>
                                    </ext2:Panel>
                                </Items>
                            </ext2:Menu>
                        </Menu>
                    </ext2:Button>
                </Items>
            </ext2:Toolbar>
        </TopBar>

        <Items>
            <ext2:Panel ID="pnlSetDefaults" runat="server">
               <Items>
  
               </Items>
            </ext2:Panel>
        </Items>
    </ext2:Window>

</body>
</html>