I found this bug when I was on singleplayer survival setting up a trap with TNT and anvils that would launch an anvil and kill the player. But I noticed it only hurt the player if the anvil fell on the player, and not when going in other directions. This does not make sense, because the anvil still hits the player.
(As corrected by StevenNL2000)

What I expected to happen:
The anvil would make contact from the side of the player, not landing on them but still damaging them because of the contact made.

What Happened:
The anvil passed through the me the player causing no damage to be delt.

Essentially it only damages player when fell upon and not when making contact from any other possible angle.

/summon FallingSand ~ ~1.25 ~ {TileID:1,Time:1,HurtEntities:1,FallHurtAmount:40,FallHurtMax:40,Motion:[0.0,0.045,-1.0]}

(put this in a command block for easy, repetitive use.)
and you can summon and mob you'd like in it's path just use NoAI:1 so it will not move.