There is more than one Duplicate. Cause it would be too easy if there was only one 🙂
If you just want to duplicate a whole object (or group) you want the duplicate under the Edit menu (Ctrl - D) or you can use Duplicate Special for added trickiness (this is also in the Edit menu. You should click it's option box to see all it's magic tricks). What you are using is Duplicate face from the Edit mesh menu. This is good for duplicating a portion of an object. It will still work the way you want though. You can just select the poly-surfaces you have made and press (shift-P) to ungroup them. Then if you like you can go back to the group and delete that. This may also turn your new objects green which I think ... ... is because you have deleted the node that references their material ... .... I think .... Anyways, you can fix this by clicking your green object, going into the render tab and clicking lambert. Now you have the duplicated object that you wanted 🙂 It is much easier to use the other duplicate from the edit menu tho.
