Choosing to use the default string "NewSubcluster" as the name of a new subcluster while an entry with the same name already exists will overwrite the old entry. Note that this is not the case when the name of the subcluster is set to something other than "NewSubcluster". Here we get an error message that an entry with that name already exists, which is the expected behavior.
*** This bug has been marked as a duplicate of bug 8084 ***