Disabling target lock on (PS3)

Okay, I have a little problem with the targeting system, hope I'll be clear enough in my explanations. (english not being my first language doesn't help -_-)

When I target a first target, the game locks on it. If I target a second target, the game will automatically target back the first target when my action is finished.

Example :
- I target a mob and begin to attack it.
- Then, I target a player to heal him/her. Once I've cast my healing spell, the game will automatically target back the mob I was attacking, even if I still want to heal the player.

It becomes really annoying when you have to switch between adds or you want to DOT several mobs, OR you have to do some emergency healing.

Is there a way to disable this feature ? Thanks in advance !

When you change targets you need to hit X once you are on the new target. When you just tab over to a new target without hitting X to lock on then it will default back to the original target.