C# Datagrid can't get sort command and item command to both work

I built a datagrid "TireDisplay", and I added this cool two-way sorting function:

void TireDisplayGrid_SortCommand(Object sender, DataGridSortCommandEventArgs e)
{
       string sortDir = "";
       if (Request.QueryString["sortOn"] == e.SortExpression)
             {
           // The sort expression matches what was sorted on last time
                       if (Request.QueryString["sortDir"] == "")
                 {
                 sortDir = "ASC";
                 }
           else if (Request.QueryString["sortDir"] == "ASC")
                 {
                 sortDir = "DESC";
                 }
           else if (Request.QueryString["sortDir"] == "DESC")
                 {
                 sortDir = "ASC";
                 }
             }
       else
       {
      // Have a new sort expression so always start out ASC
      sortDir = "ASC";
       }
     
 // Redirect back to this page with the appropriate sort expression and direction.
 Response.Redirect(Request.ServerVariables["SCRIPT_NAME"] + "?sortOn=" + e.SortExpression + "&sortDir=" + sortDir);
}

Everything works great.  Next, I needed a detail link for items in the grid.  So I added an event handler for a button column:

void GetQuote_ItemCommand(Object sender, DataGridCommandEventArgs e)
{
//get values from row where button is clicked, create a session variable, and go to detail page
string SelectedPrice = e.Item.Cells[5].Text;
Session["QuotePrice"] = SelectedPrice;
Response.Redirect("PriceQuote.aspx");
}

Everthing still works.  Then I added the button column:

<asp:ButtonColumn Text="Get a Quote" ButtonType="LinkButton" Visible="true"/>

Still OK!  But the final piece is the "OnItemCommand = GetQuote_ItemCommand" attribute of the grid.  As soon as I add this, the sort command breaks.  It now tries to activate the GetQuote_ItemCommand event, and the app breaks.

It seems like it can't distinguish between DataGridCommandEventArgs  and DataGridSortCommandEventArgs

Help!!