how to find whether ajaxautocomplete extender scroll is click or not

[tribeca_belle]

I have textbox with a ajaxautocomplete extender ,as\[code\] <asp:TextBox ID="TextBox1" onblur="callfunction()" runat="server"></asp:TextBox><ajaxToolkit:AutoCompleteExtender runat="server" ID="autoComplete1" TargetControlID="TextBox1" ServiceMethod="GetCompletionList" ServicePath="AutoComplete.asmx" MinimumPrefixLength="2" CompletionInterval="1000" EnableCaching="true" CompletionSetCount="20" CompletionListCssClass="autocomplete_completionListElement" CompletionListItemCssClass="autocomplete_listItem" CompletionListHighlightedItemCssClass="autocomplete_highlightedListItem" DelimiterCharacters=";, :" ShowOnlyCurrentWordInCompletionListItem="true"> </ajaxToolkit:AutoCompleteExtender>function callfunction(){alert()}\[/code\]Whenever the list is autopopulated,a sroll like a dropdownlist is displayed ,I want the scroll to be displayed ,If i click on the item which is populated, callfunction() function is getting not getting executed,but the problem is if i click on the scroll, callfunction() is getting executed,I dont want when user click on the scroll, the callfunction() should be executed.How to find whether scroll is click or not ??.so that i can stop callfunction to be executed that time.