When using pistons to crush leafs (using sticking pistons with logs, fence gates, slime blocks, double/triple piston extenders, etc) the saplings are pulled through the pistons and into the world. This causes tree farms to be inefficient and causes a loss of saplings resulting in the farm not being self sustaining due to the loss of saplings. The saplings should be falling to the ground (and into the hoppers) when being crushed/pushed by the pistons and not being pulled through them outside of the farm.