MariaDB 5.5.29 + Galera on Ubuntu 12.04 Crash

3 node Galera cluster - using Rsync SST. Runs fine for a few days - then does this in the middle of the night - with no load on the server - loads of RAM - no swapping:

May 1 01:54:38 site-db2 mysqld: 130501 1:54:38 [ERROR] mysqld got signal 11 ;
May 1 01:54:38 site-db2 mysqld: This could be because you hit a bug. It is also possible that this binary
May 1 01:54:38 site-db2 mysqld: or one of the libraries it was linked against is corrupt, improperly built,
May 1 01:54:38 site-db2 mysqld: or misconfigured. This error can also be caused by malfunctioning hardware.
May 1 01:54:38 site-db2 mysqld:
May 1 01:54:38 site-db2 mysqld: To report this bug, see http://kb.askmonty.org/en/reporting-bugs
May 1 01:54:38 site-db2 mysqld:
May 1 01:54:38 site-db2 mysqld: We will try our best to scrape up some info that will hopefully help
May 1 01:54:38 site-db2 mysqld: diagnose the problem, but since we have already crashed,
May 1 01:54:38 site-db2 mysqld: something is definitely wrong and this may fail.
May 1 01:54:38 site-db2 mysqld:
May 1 01:54:38 site-db2 mysqld: Server version: 5.5.29-MariaDB-mariadb1~precise
May 1 01:54:38 site-db2 mysqld: key_buffer_size=268435456
May 1 01:54:38 site-db2 mysqld: read_buffer_size=131072
May 1 01:54:38 site-db2 mysqld: max_used_connections=6
May 1 01:54:38 site-db2 mysqld: max_threads=802
May 1 01:54:38 site-db2 mysqld: thread_count=3
May 1 01:54:38 site-db2 mysqld: It is possible that mysqld could use up to
May 1 01:54:38 site-db2 mysqld: key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 2018916 K bytes of memory
May 1 01:54:38 site-db2 mysqld: Hope that's ok; if not, decrease some variables in the equation.
May 1 01:54:38 site-db2 mysqld:
May 1 01:54:38 site-db2 mysqld: Thread pointer: 0x0x0
May 1 01:54:38 site-db2 mysqld: Attempting back2trace. You can use the following information to find out
May 1 01:54:38 site-db2 mysqld: where mysqld died. If you see no messages after this, something went
May 1 01:54:38 site-db2 mysqld: terribly wrong...
May 1 01:54:38 site-db2 mysqld: stack_bottom = 0x0 thread_stack 0x40000
May 1 01:54:38 site-db2 mysqld: :0()[0x7fc4fd0682fb]
May 1 01:54:38 site-db2 mysqld: :0()[0x7fc4fcc8daa1]
May 1 01:54:38 site-db2 mysqld: :0()[0x7fc4fb501cb0]
May 1 01:54:38 site-db2 mysqld: :0()[0x7fc4f856ec65]
May 1 01:54:38 site-db2 mysqld: :0()[0x7fc4f856ee39]
May 1 01:54:38 site-db2 mysqld: :0()[0x7fc4f8570438]
May 1 01:54:38 site-db2 mysqld: :0()[0x7fc4f8627d2e]
May 1 01:54:38 site-db2 mysqld: :0()[0x7fc4f862d8b7]
May 1 01:54:38 site-db2 mysqld: :0()[0x7fc4f8633181]
May 1 01:54:38 site-db2 mysqld: :0()[0x7fc4fb4f9e9a]
May 1 01:54:38 site-db2 mysqld: :0()[0x7fc4fac2accd]
May 1 01:54:38 site-db2 mysqld: The manual page at http://dev.mysql.com/doc/mysql/en/crashing.html contains
May 1 01:54:38 site-db2 mysqld: information that should help you find out what is causing the crash.
May 1 01:54:38 site-db2 mysqld_safe: Number of processes running now: 0
May 1 01:54:38 site-db2 mysqld_safe: WSREP: not restarting wsrep node automatically
May 1 01:54:38 site-db2 mysqld_safe: mysqld from pid file /var/run/mysqld/mysqld.pid ended

Any help greatly appreciated!

Tim