mysqlのバージョンを上げたから？（MySQL_4.0.24_Debian-10sarge2）かわかんないけど、新しいテーブル作ったら_seqとかいうシーケンス用のテーブルが勝手にできとる・・・。
mysql> show tables;
+------------------+
| Tables_in_plnet |
+------------------+
| content |
| content_category |
| custom_template |
| design |
| entry |
| entry_to_tag |
| feed |
<strong>| feedback |
| feedback_seq |</strong>
| member |
| member_temporary |
| member_to_feed |
| site |
| tag |
+------------------+
14 rows in set (0.00 sec)
mysql> desc feedback;
+------------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------+---------------+------+-----+---------+-------+
| id | int(11) | | PRI | 0 | |
| name | varchar(255) | | | | |
| comment | text | | | | |
| created_at | timestamp(14) | YES | | NULL | |
+------------+---------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
mysql> desc feedback_seq;
+-------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------------+------+-----+---------+----------------+
| id | int(10) unsigned | | PRI | NULL | auto_increment |
+-------+------------------+------+-----+---------+----------------+
1 row in set (0.00 sec)_seqテーブルを削除しても元のテーブルにデータが入るとまた勝手に出来る。googleで調べてみたけどよくわからなかったな～。