Error on attempt to add second or subsequent contact in demo install

Adding the first contact was no issue. Attempts to add a second or subsequent contact generated this error with "Duplicate entry '#'" incrementing at each attempt

PDOException: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '6' for key 'PRIMARY': INSERT INTO {redhen_contact_revision} (contact_id, revision_id, author_uid, first_name, last_name, redhen_state, updated) VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2, :db_insert_placeholder_3, :db_insert_placeholder_4, :db_insert_placeholder_5, :db_insert_placeholder_6); Array ( [:db_insert_placeholder_0] => 5 [:db_insert_placeholder_1] => 6 [:db_insert_placeholder_2] => 1 [:db_insert_placeholder_3] => Test2 [:db_insert_placeholder_4] => Staff [:db_insert_placeholder_5] => 1 [:db_insert_placeholder_6] => 1357260101 ) in drupal_write_record() (line 7036 of .../includes/common.inc).