You used absolute positioning to place the UI controls using x and y coordinates—and you introduced some other Flex controls—mx:Panel, mx:Label, mx:TextArea and mx:VBox.

For example, if you add the menu as a child of the label's parent, then Flex would place the control vertically beneath that point because that is VBox's default behavior.

If the belt has a tendency to mis-track and is kept in place by the tracking profile, this generates lateral forces that in turn flex the profile and the belt.