civicrm_entity_tag entries not deleted when contact deleted

I created a new Organization, applied tags to it and verified the corresponding db entries:

mysql> select id, contact_type, display_name from civicrm_contact where id = 15393;
-------------------------------

-------------------------------

-------------------------------
1 row in set (0.00 sec)

mysql> select * from civicrm_entity_tag where entity_id = 15393;
-------------------------------------+

-------------------------------------+

-------------------------------------+
2 rows in set (0.05 sec)

I then deleted the Organization from the UI and checked th db tables once more:

mysql> select id, contact_type, display_name from civicrm_contact where id = 15393;
Empty set (0.00 sec)

mysql> select * from civicrm_entity_tag where entity_id = 15393;
-------------------------------------+

-------------------------------------+

-------------------------------------+
2 rows in set (0.04 sec)

I discovered this bug when, at the end an import, I was informed that some of the contacts could not be tagged because they already bore the relevant tag, even though I had deleted all contacts before the import. I checked the civicrm_entity_tag table and found:

mysql> select count(distinct entity_id) from civicrm_entity_tag where entity_table = 'civicrm_contact';
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---------------------------

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1 row in set (0.53 sec)

mysql> select count from civicrm_contact;
----------

----------

----------
1 row in set (0.03 sec)

So this problem had apparently been going on for a while.