At the moment, there is an error message trying to delete an inconsistant SmartObject from the category tree or in K2 Management. Only via SmartObject Tester such SMo can be deleted.

In my view, there is no reason why to check a SmartObject for consistency before deleting it. When things develop towards web-interface there needs to be a possibility to delete such SMO, maybe after a warning that not all checks can be done.