Can't select dropdown list option if there is only one option returned

I have a dynamic dropdown that is populated from sql.  The user is supposed to select an option from the dropdown, then click a search button on the form to return some results based on that selection.  It works fine if the dropdown gets populated with more than one record.  However, if only one record is returned, that one record can't be selected.  Whether you select it or just leave it alone since it's the only one, when you click the form button (search button), no results are returned b/c the dropdown selection must not be actually selected.
I've included the relevant code below.  First the DDL, then the datasource, and finally the C# code in the if (!Page.IsPostBack)

<asp:DropDownList ID="ddlSuppliers" runat="server" AutoPostBack="false" DataTextField="vendor_name" AppendDataBoundItems="true" DataValueField="vendor_ ...