asp.net Update Panel capturing Button clicks - asp.net

Question

I have a page that has an ASP.NET UpdatePanel on it. The UpdatePanel contains a repeater, and within the repeater is a command button. (please see the code example below)
When I click on the button the first time, nothing happens. But the second time I click on the same button, then I get the event I was expecting triggered. I am at a loss as to why this is, though I am sure there is a simple explanation. Any advice would be helpful.
<!-- Drivers Table -->
<asp:UpdatePanel runat="server" ID="DriverUpdatePanel" UpdateMode="Conditional" ChildrenAsTriggers="true">
<ContentTemplate>
<asp:HiddenField runat="server" ID="DriverErrors" />
<asp:Repeater ID="DriverRepeater" runat="server" OnItemDataBound="DriverRepeater_ItemDataBound" OnItemCommand="DriverRepeater_ItemCommand">
<HeaderTemplate>
<table cellspacing="0" class="section-table">
<tr>
<td class="bg_mid" colspan="7"><img src="/images/sections/drivers.png" alt="Drivers" /></td>
</tr>
<tr>
<td class="text_1 left-cell">#</td>
<td class="text_1">Name</td>
<td class="text_1">Date Of Birth</td>
<td class="text_1">Gender</td>
<td class="text_1">License #</td>
<td class="text_1">Relationship</td>
<td class="text_1" align="right"> </td>
</tr>
</HeaderTemplate>
<ItemTemplate>
<tr id="DriverRow" runat="server">
<td class="text_2 required left-cell"><asp:Label ID="DriverNumber" runat="server" Text='<%#DataBinder.Eval(Container.DataItem, "DriverNumber")%>'></asp:Label></td>
<td class="text_2 required"><asp:Label ID="DriverName" runat="server" Text='<%#DataBinder.Eval(Container.DataItem, "FirstName")%>'></asp:Label></td>
<td class="text_2 required"><asp:Label ID="BirthDate" runat="server" Text='<%#DataBinder.Eval(Container.DataItem, "BirthDate")%>'></asp:Label></td>
<td class="text_2 required"><asp:Label ID="Gender" runat="server" Text='<%#DataBinder.Eval(Container.DataItem, "Gender").ToString() == "F" ? "Female" : "Male" %>'></asp:Label></td>
<td class="text_2 required"><asp:Label ID="DriversLicenseNumber" runat="server" Text='<%#DataBinder.Eval(Container.DataItem, "LicenseInformation.DriversLicenseNumber")%>'></asp:Label></td>
<td class="text_2 required"><asp:Label ID="RelationshipToApplicant" runat="server" Text='<%#DataBinder.Eval(Container.DataItem, "RelationshipToApplicant")%>'></asp:Label></td>
<td class="text_2 right-cell" align="right"><asp:ImageButton runat="server" ID="DriverEditButton"
ImageUrl="/images/edit.jpg" AlternateText="Edit" CommandName="Edit" CausesValidation="false" /></td>
</tr>
</ItemTemplate>
<FooterTemplate>
</table>
</FooterTemplate>
</asp:Repeater>
</ContentTemplate>
</asp:UpdatePanel>

Answer 1

make UpdatePanel Mode="Conditional" and enableviewstate="true"
you not need to defined trigger and you work is done without it.