Critical Issue: Field value changes back to older value after a successful update (no replies)

I'm having a critical issue with one of my InnoDB tables. I have field that requires to constantly be updated.

1. The Update does not return any errors
2. The value sometimes is shown correctly but immediately is changed back to an older value.

The queries below were done one after the next.

mysql> select modified, current_session, ts, online, active from clients where id = 142;
+------------+-----------------+------------+--------+--------+
| modified | current_session | ts | online | active |
+------------+-----------------+------------+--------+--------+
| 1403499240 | NULL | 1384143022 | 1 | 1 |
+------------+-----------------+------------+--------+--------+
1 row in set (0.00 sec)

mysql> update clients set modified=1403905962 where id = 142;
Query OK, 1 row affected, 1 warning (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0

mysql> select modified, current_session, ts, online, active from clients where id = 142;
+------------+-----------------+------------+--------+--------+
| modified | current_session | ts | online | active |
+------------+-----------------+------------+--------+--------+
| 1403905962 | NULL | 1384143022 | 1 | 1 |
+------------+-----------------+------------+--------+--------+
1 row in set (0.00 sec)

mysql> select modified, current_session, ts, online, active from clients where id = 142;
+------------+-----------------+------------+--------+--------+
| modified | current_session | ts | online | active |
+------------+-----------------+------------+--------+--------+
| 1403499240 | NULL | 1384143022 | 1 | 1 |
+------------+-----------------+------------+--------+--------+
1 row in set (0.00 sec)

The table description is the following:

mysql> desc clients;
+-----------------+---------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------------+---------------------+------+-----+---------+----------------+
| id | bigint(20) unsigned | NO | PRI | NULL | auto_increment |
| name | varchar(50) | NO | UNI | NULL | |
| active | tinyint(4) | NO | | 1 | |
| proc | char(5) | NO | | false | |
| current_session | bigint(20) unsigned | YES | | NULL | |
| ts | bigint(20) unsigned | NO | | 0 | |
| modified | bigint(20) unsigned | NO | | 0 | |
+-----------------+---------------------+------+-----+---------+----------------+

The error seems to be happening on two records only and only for the modified field.

Every other record on the table seems to be updated successfully. I tried doing an online search for a possible cause and found absolutely nothing.

Thanks in advanced for any help on this issue.