Falling saplings from big oak tree

When I am in forest an broke only grass, big oak trees automaticly starts falling leaves and by this process starts produce oak tree sappling.
By this bug is game practically unplayable because it:
1, it decrease my FPS realy hard
2, the game has about two times slower response e.g. when i drop item I must wait around 6-7 seconds to pickup them or after than I mined stone or something else I must wait around 5-7 seconds then before block destroys.