display list

The Shape class is the most basic Flash class that supports rendering through the graphics property. The Shape hierarchy is: Shape < DisplayObject.

Some of the core classes in the Flash player are actually abstract classes. Even though you cannot instantiate these classes directly, they are still very important to understand. These classes are the parent classes for all of the visual display classes in Flash and they contribute functionality to the concrete classes that you will use in your application.

The display list is the mechanism that Flash uses to render itself onto the users screen. The display list is rooted in the Stage class and consists of all of its descendants (children, grandchildren, and so forth). DisplayObjects on the display list have a specific rendering lifecycle and event propagation mechanism. Objects which are not on the display list will not be rendered and cannot interact with user events.

More to come...

The Sprite class is one of the most basic rendering classes available in Flash. It supports the Flash drawing API, can contain other DisplayObjects, and supports user interaction events. Sprite does not have a timeline like MovieClip which makes it smaller and faster if you are not running timeline-based animations. The Sprite class is the base class which most UI components inherit from such as the UIComponent in Flex.

Flash dispatches certain standard events based on the interactions of components, especially with regards to rendering and the display list. Generally, a component receives added and addedToStage, then render events. When the component is removed it will usually receive removed and removedFromStage. Obviously, if the component is only added to another component, and the parent component is not yet on the Stage, then the "Stage" events won't fire until the topmost parent is added to the Stage.

Problem

You have a handler attached to the removedFromStage event on your component and this handler is being called unexpectedly. Sometimes called during component initialization and sometimes during resizing.