Crystal report datasource isn't updated correctly with setDataSource function in C#

Below is how I bind the DataSet to the crystal report:

DataSet dsRpt = grabData();
ReportDocument rptDoc = new ReportDocument();
rptDoc.SetDataSource(dsRpt);

The dsRpt has several DataTables which contains data to be displayed in the crystal report.

I added a sub-report in the crystal report, and I set the sub-report's datasource to a server.

But during runtime, the report will be used on different servers so I have to use the DataTable as the report's DataSource.

So here's the problem:

    No matter how the `dsRpt` changed, the newly added sub-report's data isn't changed 
    (i.e. the datasource isn't correctly binded to the sub-report)

I tried the steps in below article to help troubleshoot: http://ift.tt/1AMBpRf

1. Write the dsRpt to a xml file


2. Change the datasource of the sub-report to the xml file


3. The datasource location is successfully updated

But if I save the subreport as a main report, the DataTable in dsRpt is now correctly loaded to the report, so if I add a new subreport to main report, what I need to do to bind the DataSet's data to the subreport?