dropdownlist control confuses index values!!!

Hi to all,

I have a dropdownlist control tht is bound to a table of materials.  <asp:DropDownList ID="ddMaterialType" runat="server" Width="100%"
AutoPostBack="True" DataSourceID="SqlDataSource2" DataTextField="Description"
DataValueField="PricePerSquareMeter" CausesValidation="True">
 The fact is that there are two materials with the same PricePerSquareMeter value but with different descriptions.
When I choose for example the material B that is in the 5th index with value 50, the SelectedIndexChanged event returns the 2nd index that has the same value (50) with description A.

Can somebody please help me on this?

Thanks in advance

Stelios
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