with the registry, the object is copied, not passed by reference if I remember. This is to prevent the application from modifying the object and causing problems. The zend registry does not allow you to modify a registered object, but I think in the new release this 'feature' has been removed. So you would have to reregister the object.

I wouldnt quote myself on this as I have not used the registry much as I try to avoid it because using getInvokeArg() seems to be a better option when using the zend frontcontroller