I have upgraded from 4.0.7 to 4.1 RC2 and my treepanel failed to load. The reason being, I am using default idProperty i.e. id which has conversion field in my model. But id field is not getting set. Seeing few posts I configured my idProperty to some other value in my Model. Even though I set different value for idProperty the default value is seen in firebug. Hence id and parentsId is always undefined.