drop user leaves privileges

It looks like in certain cases DROP USER does not properly revokes all privileges before dropping the user. Test:

$ ./mtr --noreorder main.view_grant funcs_1.is_table_privileges

it will fail, because two privileges of the user dan@localhost (that was created and dropped in main.view_grant) were not revoked. Or, perhaps, information_schema.table_privileges is wrong and shows privileges that aren't there.