Disable main.index_merge_innodb with InnoDB plugin. The test case is

not ready to run with innoplug-1.0.4.

mysql-test/lib/mtr_cases.pm

@@ -494,6 +494,7 @@ sub collect_one_suite($)
       next if ($test->{'skip'} || !$test->{'innodb_test'});
       # Exceptions
       next if ($test->{'name'} eq 'main.innodb'); # Failed with wrong errno (fk)
+      next if ($test->{'name'} eq 'main.index_merge_innodb'); # Explain diff
       # innodb_file_per_table is rw with innodb_plugin
       next if ($test->{'name'} eq 'sys_vars.innodb_file_per_table_basic');
       # innodb_lock_wait_timeout is rw with innodb_plugin