[RedAjax]UpdatePanelRenderMode in RedControl

         this.Master.AjaxManager.AjaxSettings.AddAjaxSetting(P_Edit, P_GridMulti, null, UpdatePanelRenderMode.Inline);

        this.Master.AjaxManager.AjaxSettings.AddAjaxSetting(P_Edit, P_GridList, null, UpdatePanelRenderMode.Inline);

        RadAjaxLoadingPanel loading = (RadAjaxLoadingPanel)this.Master.AjaxManager.FindControl("RadAjaxLoadingPanel1");

        this.Master.AjaxManager.AjaxSettings.AddAjaxSetting(P_GridMulti, P_GridMulti, loading, UpdatePanelRenderMode.Inline);

來源參考：

https://docs.telerik.com/devtools/aspnet-ajax/controls/ajaxmanager/how-to/radajax-and-webusercontrols