UpdatePanel DefaultButton Problem

Question

Hi; I have a very interesnting problem; Please Try This;

Open an ASPX page; Add ScriptManager and UpdatePanel; Add a Label and Timer inside of UpdatePanel; Timer1.Interval=100 and timer_Tick is Label1.Text=DateTime.No.toString();

Add a ComboBox Outside Of UpdatePanel1; And Add 3 Ramdom items to ComboBox1; Add a Button again OutSide Of UpdatePanel1;

Now; set Button1 as DefaultButton like Form1.DefaultButton=Button1; Ok. Run the project; And you will see the Date information in Label1 ; But; click the ComboBox and TYR select a item from dropdownlist of ComboBox1; The dropdown list immediatly hide; Because the page focused to button1 each timer tick event so the dropdownlist of ComboBox gone;

How Can Solve This Problem ? Please.