An apparence problem appears with the lastest release (Netadvantage 2009).
Before datas, there is a grey line when the combo drop down.
It seems to be for all the combo where <combo>.Rows.Band.ColHeadersVisible property is set to false.
See this thread: Hidding Colum Header in UltraGrid and UltraComboEditor (Version 9.1.) - Infragistics Community