If user two classes with the same name in different packages (pkg.C1 and C1),
and removes nested link between pkg and C1 on diagram, both C1 classes will be
in the same root package. 
It is impossible to make this by e.g. drag-n-drop in model tree because of name
conflict.

steps:
- create class diagram.
- put package o0n diagram and name it 'pkg'
- put two class elements on diagram
- add nested link from one of them to pkg.
- name both classes 'C1'
- select nested link on diagram and delete it. Select checkbox to delete from
project.

BUG: now you have two class elements 'C1' in the same namespace.