turns out me playing with the setsortoffset didn't fix the transparency problem :S
the ground layer is added first to the world, then the trees... in any case, the issue shows up randomly...
any hints/details on how that method actually works (values I should set)?
in my last attempt, I set -2000 (negative values getting closer to the camera) for the trees and 0 for the ground layer
I'm ready for a new release with a few nice details and fixes, but would like to include this... and, while I thought of having opaque leaves, I would still have the same problem with future features.
on a side note, I'm using png's with alpha channel...