The one consistent factor with all of these messed up tree and plant renders is that the solid geometries (trunk, branches, twigs, etc)
seem to render fine. However, the parts that have been transparency mapped (leaves and needles) mess up, as if the transparency mask texture is dropping out, or some such, for those affected tiles.
Have you tried seeing what happens if you unplug the transparency mask and render a solid geometry for the leaves/needles? It
might give a better clue as to what's going on.
If anyone's pointed this out before, or if I'm stating the bleedin' obvious, my apologies