Lethian talked with me about this and that's exactly what I said.
Regrettably it's intended this way, because if you want to use the Harvester, you only want to have big sized trunks to be loaded into a trailer etc.
Therefor, the small stuff disappears. It's intended like this and we won't change it. (Nevertheless, I would like to have it stay on the ground for you to pick it up in multiplayer and use a crusher for it! )
Nevertheless, it's a [WON'T FIX] in the end and hopefully, you can understand.