Also reporting in MySQL: https://bugs.mysql.com/bug.php?id=78255
Putting foreign keys between InnoDB and MyISAM should be disallowed at schema-change time (the create table should fail) because MyISAM doesn't support foreign keys. But it is allowed if foreign keys checks are switched off.
Inserting rows then fails with "ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails" even if values are valid
This may seem like a perverse set of circumstances, but it happens quite easily when using Django South migrations.
linux debian jessie