tag a document into Nuxeo DM (with a tag that didn't exist before), then delete this document (really delete, not in trash). then if you go to the tag cloud, the tag is stil in the tag cloud, and if you click on it, you get an error message
"Exception: org.nuxeo.ecm.core.model.NoSuchDocumentException. message: No such document: 65c48b0a-f701-4a94-a1c7-032b8ea65838 "