System Information
Linux Debian 7 64bit. &

Blender Version
Tested on 2.71
and 2.72 eb464ee

Short description of error
I have an empty object for simply spawn an enemy, this work, this spawn an enemy with child.
BUT if i copy (ctrl-c ctrl-v) this empty object for spawning a new enemy, he make a new copy of the original enemy but without child.
AND if i duplicate link (alt-D) the behavior is correct (i think) this copy empty object who spawn Ennemi1, but game logic between spawn and spawn.001 are not linked.

Exact steps for others to reproduce the error
with this file:

select spawn object and duplicate it.
the new object (called spawn.001) don't spawn the object Ennemie1 but Ennemie1.001.
If we go to the layer 9 we can see a second enemy have being added (over the first).
But this new Ennemie1.001 don't have child Ennemi_gun.

comment:
I make this empty object spawn because we cant duplicate linked (Alt-D)
dont link game logic of object.

solution:

1. add game logic on data linked to the object with duplicate linked.
2. actuator Edit Object need more option like:
   • copy child ( recursive or not )
   • make new object or reuse object

I hope to have explained well.