Problem with terrain position in the world editor

Hi,

I'm new with Torque so my question may be stupid but...
When I create a terrain in the world editor (let's say size 256), to center it on 0 0 0 I have to set Transform->position to -128 -128 -512. Why not 0 0 0 ???
Besides, when I try to move the terrain using the gizmo, a little popup appear showing around x=0, y=0, z=0 while Transform->position is still set to -128 -128 -512.

Thanks for your answer

Charlie