Free/Busy queries kill the mailbox service

[SuperBeaker]

Today I have seen the mailbox service restart itself numerous times today. Example form /var/log/zimbra.log:

Sep 21 09:09:39 serenity zmmailboxdmgr[16975]: manager woke up from wait on mailboxd/JVM with pid 9391
Sep 21 09:09:39 serenity zmmailboxdmgr[11904]: wrote java pid 11904 to /opt/zimbra/log/zmmailboxd_java.pid
Sep 21 09:09:39 serenity zmmailboxdmgr[16975]: manager started mailboxd/JVM with pid 11904

/opt/zimbra/log/mailbox.log shows the following:

2009-09-21 09:09:38,757 FATAL [btpool0-81] [] system - Unable to commit database transaction.  Forcing server to abort
.

I have been able to cause this behavior directly by attempting to view the free/busy info for one particular user. Here's the steps:
1) create a new mtg in Outlook (ZCO 5.0.16.2)
2) add some other user (verify that we view another users' free/busy)
3) try to add the problem user
result: mailboxd immediately fails and I am unable to view the problem users' calendar info

The problem isn't limited to Outlook, however. If I login to the user's account via the Zimbra web client, as soon as I click on the Calendar tab, the mailbox service fails.

Any advice on what to do to resolve this problem?

[SuperBeaker]

After further troubleshooting, it looks like there are some problems in the database. The user's account that I'm having difficulty with is in mailbox group 43. Based on some information I found in /opt/zimbra/log/mailbox.log and /opt/zimbra/log/mysql_error.log, I tried the following:

mysql> use mboxgroup43;
mysql> select * from mail_item where mailbox_id=243;

MySQL crashed when I attempted this query. It appears the table is corrupt, even though zmdbintegrityreport (calling mysqlcheck) reports no problems:

[zimbra@mailhost libexec]$ /opt/zimbra/mysql/bin/mysqlcheck --defaults-file=/opt/zimbra/conf/my.cnf -S /opt/zimbra/db/mysql.sock -c -e -u root --password=fubar mboxgroup43
mboxgroup43.appointment                            OK
mboxgroup43.data_source_item                       OK
mboxgroup43.imap_folder                            OK
mboxgroup43.imap_message                           OK
mboxgroup43.mail_item                              OK
mboxgroup43.open_conversation                      OK
mboxgroup43.pop3_message                           OK
mboxgroup43.revision                               OK
mboxgroup43.tombstone                              OK

I tried to delete the offending item - this failed as well:

[zimbra@mailhost log]$ mysql mboxgroup43;
mysql> select CONCAT(id, '-', mod_content) as itemId from mail_item where id = 18011;
+--------------+
| itemId       |
+--------------+
| 18011-106100 | 
+--------------+
1 row in set (0.02 sec)

[zimbra@mailhost log]$ zmmailbox -z      
mbox> selectMailbox user@example.com
mailbox: user@example.com, size: 2.22 GB, messages: 16493, unread: 174
mbox user@example.com> deleteItem  18011-106100
ERROR: service.FAILURE (system failure: fetching item 18011)

Do I have any options besides database recovery to resolve this?