Autogen disappears into ground

In the project I'm working on (for FS9) I've used GMAX ground polygons and tweaked the .asm files to get rid of flickering and also a trick to get the default autogen show up over the textured polygons.The problem I have is that the autogen trees and houses start sinking into the ground as I climb away.Otherwise everything works fine.Here is the piece of code I used to get the autogen back:ADDCAT OBJECT_0_SCALE, 8 INSTANCE_CALL R, 0, 0, 0 BGL_JUMP_32 OBJECT_0_END R label word BGL_RETURNAnd here is a screenshot of what it looks like:I hope there's some easy fix to this.