DropDownList double-populating

I'm sure I'm doing something stupid here....

I have a drop-down-list, which I populate from an SQLdatasource set up for that pupose. It takes the currently logged-on username as a parameter, and returns records linked to that. A test of the datasource returns three records: "banana", "garlic bread", "pizza", wth associated numerical IDs (yes, this is test data).

But the dropdownlist shows six items, not three: it repeats the list. Huh?

Here's my datasource:

    <asp:SqlDataSource ID="sdsItemsDDL" runat="server" ConnectionString="<%$ ConnectionStrings:RapidConnectionString %>"
        SelectCommand="SELECT distinct [StandardItemID], [Itemname] FROM [vwrpdTeamItems] WHERE username = @username ORDER BY [Itemname]">
        <SelectParameters>
  &nbs ...