Hi Peter,
That is indeed odd. Although from what remember for each content item you have an entry to acs_objects, cr_items and cr_revisions. So I would think that test_f_0 is the one that is behaving properly if the integrity constraint is present. So in deleting you have to delete the cr_revisions entry then the cr_items and finally the acs_objects. Although I have never done any deletes since from what I remeber it was problematic so I just followed Luke P's example for having a trash folder in cr_folders. Then move the deleted items to this trash folder. Try to see if an acs_object entry is created when you create a content item.
