ASP.Net: OnSelectedIndexChanged event not firing

I had this snippet in a page:

<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional">
    <ContentTemplate>
        <table>
            <tr>
                <td>
                    <asp:ListBox ID="lst" runat="server" OnSelectedIndexChanged="lst_SelectedIndexChanged"></asp:ListBox>
                </td>

Problem was that OnSelectedIndexChanged was not firing.

Solution was to set AutoPostBack to true in the list.