Spark Dropdown Labels Disappears

I have created an application in Falsh builder 4.6 using spark controls. I have used states in the application. In one of the popup window i have drop down which shows all labels when it loads first time. But after gettting out from that state and again go to that state and open that model window, some of the labels of list are blank and are not selectable. Data provider of dropdown is an array collection. All labels appears if we scroll from mouse down key but does not appear when we scroll list with mouse.