It seems to work as I expected, so maybe I misunderstand your problem, but I will give it a chance! I created a DataSource sample with several rows in it, added a ComboBox to the root of the layout, and then just dragged the collection from the DataSource and dropped it onto the ComboBox.
, DataSource, DataContext ComboBox , . ItemsSource, DataSource ItemTemplate DisplayMemberPath, ComboBox, .
, , ItemTemplate , , , StackPanel ComboBox. ItemTemplate DisplayMemberPath , .