LinkButtons suddenly ?not defined? per Firebug, but still work fine in IE

I have some GridViews where each data row has a column in which there is a checkbox and linkbutton setup such that when the user checks or unchecks the checkbox, rather than doing an autopostback, the linkbutton (which is hidden via CSS) gets tapped to make the postback to the GridView as a RowCommand.  Here is an example from the .ascx:

  <ItemTemplate>
      <asp:LinkButton ID="ToggleReview" runat="server"
          CssClass="hidden" CausesValidation="False"
          CommandName="ToggleReview" Text="">
      </asp:LinkButton>
      <asp:CheckBox ID="ReviewedCheckBox" runat="server"
          Checked='<%# Bind("Revi ...