In the the 1.64 was added bug.
If the stone is in front of the player and this player want to lie on the ground, then, he can not do it.
In this case, all you will get - is a look into heaven in a not natural body position.
**Probably was the idea, to create the effect of obstacles for weapons, but the result, with stones is turned out, not good. **
Probably the collision model of stones, does not fully match the size of the stone.
At a distance of 1 meter weapon collides with an invisible barrier. As the human body is the position of the snake:
https://www.youtube.com/watch?v=Sgt8IYEfeVM&feature=youtu.be
As it turned out, the problem appears not only near the stones!
Thanks Lex for additional example: https://www.youtube.com/watch?v=1JWXegeMKPU&feature=youtu.be