AutoComplete ComboBox Selection Problem

Hi all, i m facing a problem with autocomplete combobox. When user type in the combo following error occurs, u can see in the pic 

When user type in the combo double list is dropped down and user cant select the right one. as mouse moves hovers on backward list. Can someone suggest the solution.? i m using .net framework 3.5 for windows forms. with the following code

cbo.DataSource = ds.Tables(0)
cbo.DisplayMember = DisplayField
cbo.ValueMember = ValueField
cbo.AutoCompleteMode = AutoCompleteMode.SuggestAppend
cbo.AutoCompleteSource = AutoCompleteSource.ListItems

Thanks in adv.