About the item renderer and item editor life cycle
Flex creates instances of item renderers and item editors as needed by your application for display and measurement purposes. Therefore, the number of instances of an item renderer or item editor in your application is not necessarily directly related to the number of visible item renderers. Also, if the list control is scrolled or resized, a single item renderer instance may be reused to represent more than one data item. Thus, you should not make assumptions about how many instances of your item renderer and item editor are active at any time.
Because Flex can reuse an item renderer, ensure that you fully define its state. For example, you use a CheckBox control in an item renderer to display a true (checked) or false (unchecked) value based on the current value of the data property. A common mistake is to assume that the CheckBox control in the item renderer is always in its default state of unchecked. Developers then write an item renderer to inspect the data property for a value of true and set the CheckBox control to checked if found.
However, you must take into account that the CheckBox may already be checked. So, you must inspect the data property for a value of false, and explicitly uncheck the control if it is checked.