rigidbody2D gravity problem

Hi,
I finished my game. while testing noticed a problem. as you can see (image) I have 3 game objects in my scene. they have rigidbody2D. they’re falling to the ground normally. but sometimes one of my game objects goes to the (0,0) . gravity doesn’t work for that game object. when this happens game doesn’t work as i want.
anyone has any idea why this happens ?
Thank you.
here is the code for spawning game objects :

GameObject go1 = Instantiate (myArray [0], new Vector2 (x,y), transform.rotation) as GameObject;

and here is the graphic of my problem :
55312-graphic.jpg

If you’re using constraints then it may be a bug that was fixed in 5.1.2 patch 3 and 5.2.0 patch 1 where the rigid-body position would occasionally be moved to the world origin.

Are you sure there is no script setting the GO3 transform position to (0, 0)?