Blender 2.53: matrix_world problem

hello, i want duplicate an object:

object = bpy.context.active_object
object_copy = bpy.context.active_object

Then when i use the matrix_world of object_copy, i work actually with the matrix_world of original copy: This is the problem

object_copy.matrix_world == object.matrix_world
But when i worte code in the console window, it’s good.
someone can help me?