Auto complete not working on combo boxes

Hi All,

We are working on the Windows application developed using  .NET 2.0 and it has following issue.

We have one WinForm which contains 3 textboxes, 2 combo boxes and 1 OK button. The tab index is set to all controls.

Following property is set to all combo boxes

AutoCompleteMode = SuggestAppend
AutoCompleteSource = ListItems


When we press tab key and bring focus on combo box then it shows AutoComplete list when we type a letter in the combo box and first item of Auto Complete list get selected according to typed letter and auto entered in the combo box.

Now if we click OK button then a pop up window appears. On close of this pop up window we are resetting the combo boxes. Now again if we bring the focus to the combo box by pressing tab key and type letter in the combo box then it shows Auto Complete  list sometimes and when it shows Auto Complete List then its first item doesn't get selected and auto entered in the combo box.

Can someone please help in this issue so that it will show Auto Complete List and first item will be selected and entered automatically ?

Thanks and Regards
Prasad