Changing player speeds causes a high enough speed to noclip through blocks.

[relative2]

If you use the function player.setSpeed(player.getSpeed() + 1); it will cause a high enough speed to noclip through small clusters of blocks. If you jump with that speed, you will be pushed into the air at high speeds, until gravity takes over and the speed is decreased and the player falls slowly.

[PAT457]

Yeah, I was playing around with this a few weeks ago, i see the results. Its the collision system. it's buggy as fuck. it doesn't require a full rewrite but it needs some fixing.