Crash in mariadb-wsrep during plugin load at startup

mariadb-wsrep server crashes when restarted after altering/changing the mysql.plugin table's storage engine to innodb.

stack trace :
..snip..
#2 0x00000000007f0fd4 in handle_fatal_signal (sig=11) at maria-5.5-galera/sql/signal_handler.cc:262
#3 <signal handler called>
#4 0x000000000077b8b2 in wsrep_commit (hton=0x7ff54645d460, thd=0x7ffff50c6920, all=false) at maria-5.5-galera/sql/wsrep_hton.cc:251
#5 0x00000000007f4074 in commit_one_phase_2 (thd=0x7ffff50c6920, all=false, trans=0x7ffff50c9680, is_real_trans=true) at maria-5.5-galera/sql/handler.cc:1443
#6 0x00000000007f3f03 in ha_commit_one_phase (thd=0x7ffff50c6920, all=false) at maria-5.5-galera/sql/handler.cc:1414
#7 0x00000000007f3975 in ha_commit_trans (thd=0x7ffff50c6920, all=false) at maria-5.5-galera/sql/handler.cc:1275
#8 0x0000000000739f96 in trans_commit_stmt (thd=0x7ffff50c6920) at maria-5.5-galera/sql/transaction.cc:383
#9 0x00000000005ca805 in close_mysql_tables (thd=0x7ffff50c6920) at maria-5.5-galera/sql/sql_base.cc:9818
#10 0x00000000006358ed in plugin_load (tmp_root=0x7ffff50cbb50, argc=0x159ac88, argv=0x7ff5464140b0) at maria-5.5-galera/sql/sql_plugin.cc:1799
.. snip..

How to repeat:
Run the attached mtr test (wsrep_plugin_load.test)
> perl mtr wsrep_plugin_load