Reproducable crash, without backtrace

On all clients with Joomla installed, there is a reproducable bug, even though they work on different databases and have different prefixes for table names. All tables are MyISAM. The problem occured before and after mysql_upgrade was performed. The query and client-side error is:

MySQL server has gone away SQL=SELECT c.*, g.name AS groupname, cc.title AS name, u.name AS editor, f.content_id AS frontpage, s.title AS section_name, v.name AS author FROM dau_content AS c LEFT JOIN dau_categories AS cc ON cc.id = c.catid LEFT JOIN dau_sections AS s ON s.id = c.sectionid LEFT JOIN dau_groups AS g ON g.id = c.access LEFT JOIN dau_users AS u ON u.id = c.checked_out LEFT JOIN dau_users AS v ON v.id = c.created_by LEFT JOIN dau_content_frontpage AS f ON f.content_id = c.id WHERE c.state != -2 ORDER BY section_name , section_name, cc.title, c.ordering LIMIT 0, 100

and MySQL's error log does not print any backtrace:

101118 6:27:25 - mysqld got signal 11 ;
This could be because you hit a bug. It is also possible that this binary
or one of the libraries it was linked against is corrupt, improperly built,
or misconfigured. This error can also be caused by malfunctioning hardware.
We will try our best to scrape up some info that will hopefully help diagnose
the problem, but since we have already crashed, something is definitely wrong
and this may fail.

key_buffer_size=2147483648
read_buffer_size=2097152
max_used_connections=8
max_threads=2002
threads_connected=2
It is possible that mysqld could use up to
key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 10318104 K
bytes of memory
Hope that's ok; if not, decrease some variables in the equation.

thd: 0x0
Attempting backtrace. You can use the following information to find out
where mysqld died. If you see no messages after this, something went
terribly wrong...
101118 06:27:25 mysqld_safe Number of processes running now: 0
101118 06:27:25 mysqld_safe mysqld restarted
101118 6:27:25 [Warning] The syntax '--log_slow_queries' is deprecated and will be removed in MySQL 7.0. Please use '--slow_query_log'/'--log-slow-file' instead.
............