current form binding implementation use property-base solution.
1.the binding is more like fx['item'] and fx['item.name'],so they are not related.
When fx['item'] changes, fx['item.name'] doesn't know it has to be reload.
2. Even we can fix issue 1 by a 'prefix' assumption, but it is still not work, because in the from, the value is loaded when it's initialization.
which means, fx['item.name'] is loaded when form initial, and no matter fx['item'] changed, the value is still not related to fx['item.name'].