Gridview disappears when clicking Edit record

I have a drop down list that controls the SelectCommand data of a gridview datasource on SelectedIndexChanged.  The issues is after the data is populated, I select the Edit option for a record, the gridview disappears.  I have tried making it a session variable, but the same thing happens.

  protected void ddlTerm_SelectedIndexChanged(object sender, EventArgs e)
{        
SqlDSApp.SelectCommand = ("SELECT [RFSID], [DID], [DSubmitDate] FROM [Demo] WHERE (DSubmitTerm = '" + ddlTerm.SelectedValue + "')");

            gvRSStudents.DataBind();       
}

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Thanks for any help!