main.ctype_upgrade failed in buildbot, error upon mysql_upgrade

main.ctype_upgrade 'innodb'              w4 [ fail ]

        Test ended at 2018-07-30 14:20:16

CURRENT_TEST: main.ctype_upgrade

mysqltest: At line 177: exec of 'D:\win32-debug\build\client\Debug\mysql_upgrade.exe --defaults-file=D:/win32-debug/build/mysql-test/var/4/my.cnf --force 2>&1' failed, error: 1, status: 1, errno: 0

Output from before failure:

Phase 1/7: Checking and upgrading mysql database

Processing databases

mysql

mysql.column_stats                                 OK

mysql.columns_priv                                 OK

mysql.db                                           OK

mysql.event                                        OK

mysql.func                                         OK

mysql.gtid_slave_pos                               OK

mysql.help_category                                OK

mysql.help_keyword                                 OK

mysql.help_relation                                OK

mysql.help_topic                                   OK

mysql.host                                         OK

mysql.index_stats                                  OK

mysql.innodb_index_stats                           OK

mysql.innodb_table_stats                           OK

mysql.plugin                                       OK

mysql.proc                                         OK

mysql.procs_priv                                   OK

mysql.proxies_priv                                 OK

mysql.roles_mapping                                OK

mysql.servers                                      OK

mysql.table_stats                                  OK

mysql.tables_priv                                  OK

mysql.time_zone                                    OK

mysql.time_zone_leap_second                        OK

mysql.time_zone_name                               OK

mysql.time_zone_transition                         OK

mysql.time_zone_transition_type                    OK

mysql.user                                         OK

Phase 2/7: Installing used storage engines... Skipped

Phase 3/7: Fixing views

Phase 4/7: Running 'mysql_fix_privilege_tables'

The result from queries just before the failure was:

< snip >

mtr

mtr.global_suppressions                            OK

mtr.test_suppressions                              OK

performance_schema

test

test.maria050313_ucs2_croatian_ci_def              Needs upgrade

test.maria050313_utf8_croatian_ci                  Needs upgrade

test.maria050533_xxx_croatian_ci                   Needs upgrade

test.maria100004_xxx_croatian_ci                   Needs upgrade

test.mysql050614_xxx_croatian_ci                   OK

Repairing tables

test.maria050313_ucs2_croatian_ci_def              OK

test.maria050313_utf8_croatian_ci                  OK

test.maria050533_xxx_croatian_ci                   OK

test.maria100004_xxx_croatian_ci                   OK

Phase 7/7: Running 'FLUSH PRIVILEGES'

OK

# Running mysql_upgrade for the second time

# This should report OK for all tables

More results from queries before failure can be found in D:\win32-debug\build\mysql-test\var\4\log\ctype_upgrade.log