INSTALL PLUGIN Spider SONAME 'ha_spider.so';

--error ER_BAD_TABLE_ERROR

DROP TABLE t1;

Leads to:

CURRENT_TEST: main.test

mysqltest: At line 3: query 'DROP TABLE t1' succeeded - should have failed with errno 1051...

The DROP TABLE t1 should fail (and thus the MTR testcase should succeed as --error ER_BAD_TABLE_ERROR was specified). However, it succeeds. There are possibly other more serious variations/implications of this scenario. If a code check shows that the issue is limited to an incorrect "Query OK" return only, the priority can be lowered.