mysql is not using the mentioned foreign key constraint name

I faced a strange situation, so I thought to share it with you, in case someone else finds himself in similar situation.

I added a column to an existing table in MySQL. I also added a foreign key constraint on that column. So what is strange about that. Let me show you.

First of all let me display the original structure of the table.

mysql> SHOW CREATE TABLE T_DEVICE_RESULTANTSTATE\G
*************************** 1. row ***************************
       Table: T_DEVICE_RESULTANTSTATE
Create Table: CREATE TABLE `t_device_resultantstate` (
  `RESULTANTSTATEID` int(11) NOT NULL AUTO_INCREMENT,
  `RESULTANTSTATE` blob,
  `DEVICEID` int(11) NOT NULL,
  `CREATEDBY` varchar(50) NOT NULL DEFAULT 'ADMIN',
  `CREATEDATE` datetime DEFAULT NULL,
  `MODIFIEDBY` varchar(50) NOT NULL DEFAULT 'ADMIN',
  `MODIFIEDDATE` datetime DEFAULT NULL,
  PRIMARY KEY (`RESULTANTSTATEID`),
  KEY `FK_T_DEVICE_RESULTANT_STATE_T_DEVICE` (`DEVICEID`),
  CONSTRAINT `FK_T_DEVICE_RESULTANT_STATE_T_DEVICE` FOREIGN KEY (`DEVICEID`) REFERENCES `t_device` (`DeviceID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

Now the SQL statement that I used to alter the structure of the above table.

mysql> alter table t_device_resultantstate add devicelockingid int;
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> alter table t_device_resultantstate add foreign key fk_t_dresultantstate_t_dlocking(devicelockingid) references t_device_locking (devicelockingid) on delete no action on upda
te cascade;
Query OK, 0 rows affected (0.05 sec)
Records: 0  Duplicates: 0  Warnings: 0

No error and the new column and foreign key added successfully. But what is strange here is that I provided fk_t_dresultantstate_t_dlocking as foreign key contraint name but MySQL is using its auto generated value t_device_resultantstate_ibfk_1 as constraint name, although the associated key name is as defined in the SQL statement. See the table structure below.

mysql> SHOW CREATE TABLE T_DEVICE_RESULTANTSTATE\G
*************************** 1. row ***************************
       Table: T_DEVICE_RESULTANTSTATE
Create Table: CREATE TABLE `t_device_resultantstate` (
  `RESULTANTSTATEID` int(11) NOT NULL AUTO_INCREMENT,
  `RESULTANTSTATE` blob,
  `DEVICEID` int(11) NOT NULL,
  `CREATEDBY` varchar(50) NOT NULL DEFAULT 'ADMIN',
  `CREATEDATE` datetime DEFAULT NULL,
  `MODIFIEDBY` varchar(50) NOT NULL DEFAULT 'ADMIN',
  `MODIFIEDDATE` datetime DEFAULT NULL,
  `devicelockingid` int(11) DEFAULT NULL,
  PRIMARY KEY (`RESULTANTSTATEID`),
  KEY `FK_T_DEVICE_RESULTANT_STATE_T_DEVICE` (`DEVICEID`),
  KEY `fk_t_dresultantstate_t_dlocking` (`devicelockingid`),
  CONSTRAINT `t_device_resultantstate_ibfk_1` FOREIGN KEY (`devicelockingid`) REFERENCES `t_device_locking` (`devicelockingid`) ON DELETE NO ACTION ON UPDATE CASCADE,
  CONSTRAINT `FK_T_DEVICE_RESULTANT_STATE_T_DEVICE` FOREIGN KEY (`DEVICEID`) REFERENCES `t_device` (`DeviceID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

I found out that the correct way to specify foreign key constraint in MySQL table is as follows:
 

alter table t_device_resultantstate add devicelockingid int;
alter table t_device_resultantstate add CONSTRAINT fk_t_dresultantstate_t_dlocking foreign key (devicelockingid) references t_device_locking (devicelockingid) on delete no action on update cascade;

You can check it by issuing SHOW CREATE TABLE T_DEVICE_RESULTANTSTATE\G on mysql prompt.