Steps to reproduce

1. run attached zul and vm
2. click a navitem, the command executed
3. switch to "Menu Heirarchy 2"
4. click a navitem

Actual result

no command executed and a javascript error occurred.

2zkmax.nav.wpd:5 Uncaught TypeError: Cannot read property 'bindLevel' of nullzkmax.nav.Navbar.zk.$extends.closeNav @ zkmax.nav.wpd:5zkmax.nav.Navbar.zk.$extends.setSelectedItem @ zkmax.nav.wpd:5zkmax.nav.Navitem.zk.$extends.doSelect_ @ zkmax.nav.wpd:8f @ zk.wpd:21(anonymous function) @ zk.wpd:21bH.event.dispatch @ zk.wpd:9bH.event.add.cb.handle @ zk.wpd:9