Expanded propery not working if using ViewModel

[Joshua]

I was using your datasource expample for binding to my treeview and it picked up the expanded property:true no problem.
Then I switched to using your viewodels and the tree bound fine except for the epanded property.
It seems to ignore the epxanded property if you use ViewModel.

I am using the beta version 2012 Q2.

Is there soemthing different you have to do if using viewmodels?