database - MySQL InnoDB constraint does not work -

i stumble upon strange behavior innodb constraint, , cannot find cause of it.
have tables data.
below listed structures:

 create table `contents` (   `id` int(10) unsigned not null auto_increment,   `title` varchar(255) default null,   primary key (`id`),   key `title` (`title`) ) engine=innodb default charset=utf8;  create table `fields` (   `id` int(10) unsigned not null auto_increment,   `name` varchar(45) not null,   `type` varchar(45) not null,   primary key (`id`),   unique key `nameunique` (`name`),   key `name` (`name`),   key `type` (`type`) ) engine=innodb default charset=utf8;  create table `datatable` (   `id` bigint(20) unsigned not null auto_increment,   `value` double not null,   primary key (`id`),   unique key `value_unique` (`value`) ) engine=innodb default charset=utf8;  create table `content_data` (   `content_id` int(10) unsigned not null,   `field_id` int(10) unsigned not null,   `data_id` bigint(20) unsigned not null,   primary key (`content_id`,`field_id`,`data_id`),   key `fk_content_data_2_idx` (`field_id`),   key `fk_content_data_3_idx` (`data_id`),   constraint `fk_content_data_1` foreign key (`content_id`) references `contents` (`id`) on delete cascade on update cascade,   constraint `fk_content_data_2` foreign key (`field_id`) references `fields` (`id`) on delete cascade on update cascade,   constraint `fk_content_data_3` foreign key (`data_id`) references `datatable` (`id`) on delete cascade on update cascade ) engine=innodb default charset=utf8; 

now, let's execute 2 queries:
first query:

 mysql> select * `datatable` id=21318; empty set (0.00 sec) 

we got empty set , ok since datatable in fact has no row id=21318
second query:

 mysql> select * `content_data` data_id=21318; +------------+----------+---------+ | content_id | field_id | data_id | +------------+----------+---------+ |        552 |       35 |   21318 | +------------+----------+---------+ 1 row in set (0.00 sec) 

here, last query give result data_id=21318. wtf!

---

how explain situation?
why constraint not work?
idea, thanks.

if call made

set foreign_key_checks=0; 

then fk checks turned off. knows, may state of system right now. have them turned on with

set foreign_key_checks=1; 

note following. turning checks on not re-validate referential integrity. 1 needs alter table that.

simply publishing schema little safeguarded.

meaning, turn off constraints, use system, delete data, load data infile (in short mess data), run off stackoverflow schema , "gosh how did happen".

and doesn't matter state system in now. matters in then.