For example, we have an AbstractTreeModel with 3 items:

Root
- A (open)
- B (closed)

So there is one open path: [0]

If item A is removed from model and corresponding TreeDataEvent.INTERVAL_REMOVED is fired, AbstractTreeModel still retains an open path.
Also, if a new item X is inserted before A and corresponding TreeDataEvent.INTERVAL_ADDED is fired, AbstractTreeModel considers X as opened and A as closed (the path [0] is not updated).