Setting set_enableAjax(false) on on ajax request start

Question

I have a RadComboBox inside rad grid template column, grid have its own ajax setting.

I need to do a standard postback on OnSelectedIndexChanged so on ajax manager OnRequestStart i am setting set_enableAjax(false) when the sender is RCBExport.

Now i click on combo box, change the selected value, this triggers RCBExport_SelectedIndexChanged. Which is correct. After this i click on any grid item command item(ExportAll in this case) this should trigger grids OnItemCommand but instead it triggers OnClientSelectedIndexChanged_RCBExport until i reload the page.

---

  <telerik:RadGrid ID="RGGrid" runat="server" OnItemCommand="RGGrid_ItemCommand">
            <MasterTableView>
                <Columns>
                 <telerik:GridTemplateColumn> 
                      <ItemTemplate>
                           <asp:ImageButton ID="ImgExportAll" runat="server" CommandName="ExportAll"></asp:ImageButton>
                          <telerik:RadComboBox runat="server" ID="RCBExport"  OnSelectedIndexChanged="RCBExport_SelectedIndexChanged">
                                <Items>
                                    <telerik:RadComboBoxItem Text="Export1" Value="0" />
                                    <telerik:RadComboBoxItem Text="Export2" Value="1" />
                                </Items>
                            </telerik:RadComboBox>
                        </ItemTemplate>
                    </telerik:GridTemplateColumn>
                </Columns>
            </MasterTableView>
        </telerik:RadGrid>

I tired it without set_enableAjax and it work fine.