Single Table Inheritance and JSON

[ghost]

Hi,
I created an abstract node class (Application_Model_Node) and 3 classes inherit from it.
This works quite well, but when I used JSON, then the method addChild doesn't update all right values.
I tried to debug and found that it has something to do with my Single Table Inheritance.
E.g. if I exchange in the method shiftRLRange of NodeWrapper the line
->update(get_class($this->getNode()), 'n')
by
->update('Application_Model_Node' , 'n')
then it works again.
Is this a bug on NestedSet or is NestedSet not supposed to work with the combination SingleTableInheritance/JSON or can I do something different?
Thanks,
Ben