The selected TreeItem does not updated if value changed, even I use the next code:
EventType<TreeItem.TreeModificationEvent<Object>> eventType = TreeItem.valueChangedEvent();
TreeItem.TreeModificationEvent<Employee> fireItem = new TreeItem.TreeModificationEvent<>(eventType, selected);
treeView.fireEvent(fireItem);

Start the file with argument "event" to send the event, or try without them. Select child node, change value, press the button.
The value is updated only by collapse/expand the root node.

src: http://ubuntuone.com/5hTUmcqthNUYu0aTZJtprC