Using subreport inside a table/tablix cell

In my application I have a report with one subreport contained inside a table cell.  Within the SubreportProcessing event handler I supply a different set of data foreach instance of the subreport.  In VS 2008 this worked okay.  However, when I switched over to VS2010 and upgraded the report file format, the behavior changed.  All subreport instances in the master table now contain the data that I supplied for the first table row.

void LocalReport_SubreportProcessing(object sender, SubreportProcessingEventArgs e)
{
 // _index is a global variable that is reset to zero in the DataBind procedure.
 Trip currentTrip = _trips[_index];

 e.DataSources.Add(new ReportDataSource("DataSourceName", currentTrip.Items));

 _index++;
}

Is this the intended behavior?  How can I now supply different datasets for multiple instances of the same subreport inside a table?

Thanks in advance.

Vladislav