a difficult situation on tree modelling and rendering

i’ve got a heavy scene with couple of layers of trees spreading around based on one group of two leaves particle system, things all go right until it comes to render, the rendering is actually fine but then you’ll notice since the leaf group is duplicated (by shift+d) into each different layer, every time the render out on leaves is different from each other, to elaborate a bit more, when you’ve got the tree and leaf group on layer 1, it renders with certain amount of leaves for sure, after you duplicate the tree and hence the leaf gourp (due to the reason i need to render them out separately) into layer 2, all trees render with some other looking of leave (mainly on the amount), so it’s like every time you duplicate the original leaf group(which contains two leaves sample to establish the particle leaf system) it gives a different looking on leaves spread around the tree; unfortunately, the dupligroup doesn’t work on this situation, the leaves wont show up on the tree, of course i can always convert the particle modifier to sort this but it’s not flexible and quite tedious.
hope you guys understand what i describe here, if anything’s not clear, i’d explain a bit more, cheers.