Chart report ignores new data source

Not sure what you mean by it not being clear which viewer is in use. It's the Telerik report viewer. Here is the registration from the .aspx page:

<%@ Register Assembly="Telerik.ReportViewer.WebForms, Version=10.1.16.615, Culture=neutral, PublicKeyToken=a9d7983dfcc261be" Namespace="Telerik.ReportViewer.WebForms" TagPrefix="telerik" %>

and the element:

             <telerik:ReportViewer ID="ReportViewer1" runat="server" Width="600" Height="400" ParametersAreaVisible="False" ShowNavigationGroup="False" ShowHistoryButtons="False" ShowParametersButton="False"></telerik:ReportViewer>
                 <script type="text/javascript">
                     ReportViewer.prototype.OnReportLoadedOriginal = ReportViewer.prototype.OnReportLoaded;
   
                     ReportViewer.prototype.OnReportLoaded = function () {
                         this.OnReportLoadedOriginal();

                         var iframeID = this.clientID + "ReportFrame";

                         var iframe = document.getElementById(iframeID);

                         var wnd = iframe.contentWindow;

                         wnd.NavigateToUrl = function (url) {
                             window.radopen(url, "", 1025, 800);
                         };
                     }
                 </script>

The problem is, reportviewer1.RefreshReport does nothing. I have to manually click the refresh button on the viewer to refresh the report, and display the data from the dataset I just used:

     Dim graph = DirectCast(oReport.Items.Find("Graph1", True)(0), Telerik.Reporting.Graph)
        graph.DataSource = ds

        oReportSource.ReportDocument = oReport     ' this is the report with the graph on it
        ReportViewer1.ReportSource = oReportSource ' I set the report viewer's report source
        ReportViewer1.RefreshReport()   ' Does nothing