during some insert/update/delete/create/drop tables in 2 threads, the value of all auto_increment columns of all tables having auto-inc is going negative until next restart of mysqld! I am never explicitly setting the value of this column.

+--------------+-----------+----------------------+
| Index_length | Data_free | Auto_increment |
+--------------+-----------+----------------------+
| 2768896 | 1536 | 18446744073709544176 |
| 2293760 | 1600 | 18446744073709551591 |
| 2785280 | 1536 | 18446744073709533706 |
| 2818048 | 1536 | 18446744073709514555 |
| 2506752 | 1600 | 18446744073709546776 |
| 2801664 | 1536 | 18446744073709479735 |
| 2539520 | 1536 | 18446744073709530170 |
| 0 | 1664 | NULL |
| 0 | 0 | NULL |
+--------------+-----------+----------------------+

<restart>

+--------------+-----------+----------------+
| Index_length | Data_free | Auto_increment |
+--------------+-----------+----------------+
| 2768896 | 1536 | 8371318 |
| 2293760 | 1600 | 8337988 |
| 2785280 | 1536 | 8373409 |
| 2818048 | 1536 | 8286416 |
| 2506752 | 1600 | 8384250 |
| 2801664 | 1536 | 8376923 |
| 2539520 | 1536 | 2147483648 |
| 0 | 1664 | NULL |
| 0 | 0 | NULL |
+--------------+-----------+----------------+

will post more details soon.