When I set a path to obj_001 for a population's object maker, default shaders are created within the parts shader that match the texture and material associated with obj_001. If I go back to the external program (speedtree, for example) and make changes to obj_001, save it as obj_v002 and try re-pathing it in that same population node in terragen, the default shaders don't get fully updated. The color image will update to obj_v002, but the diffuse and reflectivity values will remain the same as obj_v001.
I can get around this by making a new population node every time I need to make an update to the object being populated, but it gets to be time consuming. Hopefully this can be fixed at some point. Currently I'm running 4.1.00 frontier
Thanks,
Matt