Start two Percona servers and create database test.

Then use the following two scripts to create the table (create-MYISAM.sql and create-MEMORY.sql). The only difference is that the engine is different.

Then the same select statement is executed separately, and the returned results are inconsistent. 

MYISAM:

Empty set (0.00 sec)

MEMORY:

------------------------+

------------------------+

------------------------+

4 rows in set (0.00 sec)

These are simple database operations, there should not be such inconsistent behavior.