Steps:
1. run following code;
2. Expand "Second parent"
3. Select "Child 2"
4. Expand "First parent"

You get
a) visual selection for child 2.
b) getSelectionModel().getSelectedItem() will return null
c) visual focus for second parent. It seems to be expected behavior

public class TreeViewSelection extends Application {
    @Override
    public void start(Stage stage) throws Exception {
       final TreeView tree;
        stage.setScene(new Scene(new Group(tree = TreeViewBuilder.create().showRoot(false)
                .root(TreeItemBuilder.create()
                        .children(
                                TreeItemBuilder.create().value("First parent")
                                        .children(new TreeItem("Child 1")).build(),
                                TreeItemBuilder.create().value("Second parent")
                                        .children(new TreeItem("Child 2")).build()
                        ).build())
                .build())));
        tree.getSelectionModel().selectedItemProperty().addListener(new InvalidationListener() {
            @Override
            public void invalidated(Observable observable) {
                System.out.println(tree.getSelectionModel().getSelectedItem());
            }
        });
        stage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }
}


//////output
TreeItem [ value: Child 2 ]
null