Hello,
You can use the event AfterCloseUp of  ClientSideEvents tag and force post back with JS code.

ASXP of templated column:
<Columns>
                        <igtbl:TemplatedColumn Width="100">
                            <CellTemplate>
                                <igcmbo:WebCombo ID="WebCombo1" DataSourceID="SqlDataSource1" runat="server" Width="100">
                                    <ClientSideEvents AfterCloseUp="ACU" />
                                </igcmbo:WebCombo>
                            </CellTemplate>
                        </igtbl:TemplatedColumn>

JS cede:

 <script type="text/javascript">

   function ACU(cmboID) {

            var combo = igcmbo_getComboById(cmboID);
            __doPostBack(combo,"");
            //debugger;
        }

</script >

I hope this helps.