Torque to Blender, problem of transparency/Z-buffer.

I am part of a small indie dev team for racing game where my role is to do assets. I've encountered one problem though and was wondering if you guys have experiences of similar (yes I did use search first, but with no succes). When I have made an item with more than 1 object with transparent texture it shows rather fine in blender (all planes are 1-sided but that doesn't matter). Problem comes with exporting to DTS and viewing this model in our game engine (Torque) with ShowToolPro however. Z-buffer seems to be doing it all wrong showing trought the parts it shouldn't. Here's picture of what I mean:



Right, I was able to correct trunk showing trought by placing leafs on layer 2 and trunk on layer 1, however what's still matter is that each of my leaf part has 4 intersecting planes with same transparent texture (so you can see texture from all angles). These leafs ain't z-buffered correctly but show "inside out" like this:

This is how it looks:

This is how it should look:

(first image demonstrates this too). I'm using latest blender, alphamapped super PNG for texture and been searching, trying and crying for total of 16 hours with this problem. So I turn to you my good fellow Blender modellers, any idea at all what I might be doing wrong/don't know. I guess I'm just too green/noob to figure this one out, would be lovely to carry on with my work =)

ps. here's zip file if you want to try/see yourself www.venomlemon.com/bush.zip