Only seems to happen in SSP:
EntityDart impact is detected a in the server thread and the impact code is fired; its velocity is set to zero.
On the client thread, the entity keeps moving, but hits the wall and as a result falls down, when it hits the ground it fires the impact code, setting the position of the hooked grapple to where it fell. Shortly afterwards it is synced from the server thread en shifts to where it impacted in the server thread.
However the impact location of where the dart fell is still used in the physics calculation leading to a different movement as what would be expected from rendering.