DragBroken is called if a mouse drag is interrupted by the system. As noted above, when a mouse button is held, MouseEvent will continue to be called, even if the mouse is outside the Area. On some systems, this behavior can be stopped by the system itself for a variety of reasons. This method is provided to allow your program to cope with the loss of the mouse in this case. You should cope by cancelling whatever drag-related operation you were doing.
Note that this is only generated on some systems under specific conditions. Do not implement behavior that only takes effect when DragBroken is called.