Selection problem with ComboBox

I have a TDBLookupComboBox which looks at a table with 3 part primary key.
The problem is when I select a value in the drop down box it high  lights
all values with the same value that I have made the Key Field.
The key field has to be set to this because the datafield is the same.
I was wondering if it is posible to set the combo box so it will only select
the row clicked on in a case like this?

Thanks in advance
Richard