I have a crash similar to the one reported in the bug even after upgrade to 5.6.15-25.5:

BF-BF X lock conflict
RECORD LOCKS space id 6910 page no 97 n bits 160 index `GEN_CLUST_INDEX` of table `db`.`tbl_without_pk` trx id 3254927279 lock_mode X locks rec but not gap
08:12:36 UTC - mysqld got signal 6 ;
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.
Please help us make Percona XtraDB Cluster better by reporting any
bugs at https://bugs.launchpad.net/percona-xtradb-cluster

key_buffer_size=8388608
read_buffer_size=131072
max_used_connections=246
max_threads=1002
thread_count=46
connection_count=46
It is possible that mysqld could use up to 
key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 407967 K  bytes of memory
Hope that's ok; if not, decrease some variables in the equation.

Thread pointer: 0x7fb760000990
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...
stack_bottom = 7fb7a6ef8d88 thread_stack 0x40000
/usr/sbin/mysqld(my_print_stacktrace+0x35)[0x902645]
/usr/sbin/mysqld(handle_fatal_signal+0x4c4)[0x6801e4]
/lib64/libpthread.so.0(+0xfae0)[0x7fcec84c2ae0]
/lib64/libc.so.6(gsignal+0x35)[0x7fcec6934ba5]
/lib64/libc.so.6(abort+0x17b)[0x7fcec69364bb]
/usr/sbin/mysqld[0x9950db]
/usr/sbin/mysqld[0x99973f]
/usr/sbin/mysqld[0x999ae3]
/usr/sbin/mysqld[0xa0b4ff]
/usr/sbin/mysqld[0xa11679]
/usr/sbin/mysqld[0x968857]
/usr/sbin/mysqld(_ZN7handler11ha_rnd_nextEPh+0x9c)[0x5c087c]
/usr/sbin/mysqld(_ZN14Rows_log_event24do_table_scan_and_updateEPK14Relay_log_info+0x198)[0x89fec8]
/usr/sbin/mysqld(_ZN14Rows_log_event14do_apply_eventEPK14Relay_log_info+0xd8f)[0x8a59df]
/usr/sbin/mysqld(_ZN9Log_event11apply_eventEP14Relay_log_info+0x68)[0x8a6c38]
/usr/sbin/mysqld(_Z14wsrep_apply_cbPvPKvmjPK14wsrep_trx_meta+0x5ce)[0x5bd38e]
/usr/lib64/libgalera_smm.so(_ZNK6galera9TrxHandle5applyEPvPF15wsrep_cb_statusS1_PKvmjPK14wsrep_trx_metaERS6_+0xb1)[0x7fce5c60e211]
/usr/lib64/libgalera_smm.so(+0x1ab345)[0x7fce5c647345]
/usr/lib64/libgalera_smm.so(_ZN6galera13ReplicatorSMM9apply_trxEPvPNS_9TrxHandleE+0x283)[0x7fce5c6481b3]
/usr/lib64/libgalera_smm.so(_ZN6galera13ReplicatorSMM11process_trxEPvPNS_9TrxHandleE+0x45)[0x7fce5c648aa5]
/usr/lib64/libgalera_smm.so(_ZN6galera15GcsActionSource8dispatchEPvRK10gcs_actionRb+0x2c9)[0x7fce5c623a89]
/usr/lib64/libgalera_smm.so(_ZN6galera15GcsActionSource7processEPvRb+0x63)[0x7fce5c623f63]
/usr/lib64/libgalera_smm.so(_ZN6galera13ReplicatorSMM10async_recvEPv+0x93)[0x7fce5c642db3]
/usr/lib64/libgalera_smm.so(galera_recv+0x23)[0x7fce5c657aa3]
/usr/sbin/mysqld[0x5be11f]
/usr/sbin/mysqld(start_wsrep_THD+0x3fe)[0x5ae42e]
/lib64/libpthread.so.0(+0x7ddb)[0x7fcec84baddb]
/lib64/libc.so.6(clone+0x6d)[0x7fcec69e2a1d]

Trying to get some variables.
Some pointers may be invalid and cause the dump to abort.
Query (0): is an invalid pointer
Connection ID (thread ID): 12
Status: NOT_KILLED