I've been noticing this bug since the first few months i've been playing, but i haven't said anything until now as its not gamebreaking and minor. But I still think I should throw it out there since nobody else has.
Whenever I chop a tree into logs before it hits the ground (haven't tested after it hits the ground yet) rarely some of the logs fall underneath the ground and I only get 1 or 2 logs from the tree. This is more noticeable when I have a large tree farm. This happens both in survival and semi-creative mode.
I tested how often by building a dirt platform above ground, planting trees, waiting, then chopping. I notice anywhere between 2-5% of the time this happens.