Creating tagged items with acts_as_taggable_on rollsback incorrectly

Described in https://github.com/mbleigh/acts-as-taggable-on/issues/1068, and https://github.com/mbleigh/acts-as-taggable-on/pull/809

Worst case

Transactions are rolled back silently

Probable case

The ROLLBACK statement gets issued against the wrong database. Postgres emits a warning that there is no transaction in progress