activerecord/test/cases/relations_test.rb fails on mysql and sqlite when executed separately from other tests

Everything is ok when running:

rake test_sqlite3
rake test_mysql

but executing

rake test_sqlite3 TEST=test/cases/relations_test.rb
rake test_mysql TEST=test/cases/relations_test.rb

leads to error:

# Mysql
1) Failure:
test_any(RelationTest) [test/cases/relations_test.rb:643]:
4 instead of 3 queries were executed.
Queries:
SELECT COUNT(*) FROM `posts` 
SHOW TABLES
SELECT COUNT(*) FROM `posts`  WHERE `posts`.`id` IS NULL
SELECT `posts`.* FROM `posts` .
<3> expected but was
<4>.

#Sqlite
1) Failure:
test_any(RelationTest) [test/cases/relations_test.rb:643]:
4 instead of 3 queries were executed.
Queries:
SELECT COUNT(*) FROM "posts" 
          SELECT name
          FROM sqlite_master
          WHERE type = 'table' AND NOT name = 'sqlite_sequence'

SELECT COUNT(*) FROM "posts"  WHERE "posts"."id" IS NULL
SELECT "posts".* FROM "posts" .
<3> expected but was
<4>.