A general rule of computer science is individually unlikely events become likely to occur when code paths are run over 100s of thousands of times.

In general here - perhaps the object manager might get told that instance 10 exists so it registers 10 new instances and only then starts dispatching the calls to the object browser model.  More specifically since the ```beginInsertRows``` call expects the number of rows in the tree to be passed that is what we should be doing by introspecting the model.