Bug #1827 Replication is severly delayed

Description:
On some occasions, my replicated slave encouteres a delay which I believe may be causes by a bug in MySQL. The replication stops for several minutes (10 min at maximum) and then starts again. I found out that it happens when there's a "Waiting for release of readlock" line in the MySQL process list. It looks like this:

| 1      | system user |           |      | Connect | 779340 | Waiting for master to send event |                                                                                                      |
| 2      | system user |           | ubox | Connect | 857    | Waiting for release of readlock  | UPDATE user_email SET last_used = NOW(), last_client_ip = 'xxx.175.36.79' WHERE reg_user_id = 279784 |
| 580178 | root        | localhost | ubox | Query   | 212    | Writing to net                   | SELECT /*!40001 SQL_NO_CACHE */ * FROM `reg_user_data`                                               |

But there's no process accesing the user_email table. What could be the problem?

How to repeat:
Don't know.

Check that you do not have a backup of some sort running (via mysqldump for instance) that is acquiring read locks on the table.  Otherwise, use mysqlbinlog and see what other statements may be causing the lock.

I am, otherwise, unable to repeat this behavior.

Thank you.

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