Strange behaviour of scrolling in flex mobile

working on flex mobile list. list is represented using itemrenderer. here is
the itemrendeerer..

<s:Image id="img" x="30" y="50"/>
<s:Label id="nameLbl" width="100%" height="100%" text="Label"
textAlign="center" verticalAlign="middle"/>
<s:Button id="checkMarkLabel" label="+" height="100%" />*

on selected::

protected function onClicked(event:MouseEvent):void

if(checkMarkLabel.label =="✓")

checkMarkLabel.label = "+";

else if(checkMarkLabel.label == "+" )

checkMarkLabel.label = "✓";
trace("id::"+event.currentTarget.data.id)
//FlexGlobals.topLevelApplication.selectedId =
event.currentTarget.data.id;

}*

<http://apache-flex-users.2333346.n4.nabble.com/file/n7212/scrolligng_issuue.png>
the image gives you the clear picture. after selecting some items in the
list,if i scroll the list,the checked items gets unchecked and the unchecked
items gets checked.any answer is appreciable..