Auto source combo losing text

I am working in C# (Windows application).
I have a combo box with the following properties:

 -  Auto complete mode=suggest append
 -  Auto Complete source :List items
 -  Drop down style: Drop down;

I have set data source, value member, display member to this combo.

Then what is my problem is that when I type some letters it is appended, its ok.
And when I am leaving the combo after selecting it, the selected text become cleared.
Any one of you have solution for this?