I just found a bug in the ajax auto complete extender. This does not allow multiple instances of the control to appear in the same web page. If you have it with animation Like the element below.It should have a unique name per control. Otherwise you will lose control. When one of the controls is selected it will ends up firing the same event for both the controls.
Solution: You can avoid using animation or css elements form the extenders or use different names for css classes used by them.
found a good work around here :http://forums.asp.net/t/1362679.aspx