Spiders can hit the player from beneath a block

What I expected to happen was...:
Being that there is a full layer of blocks in-between the spider and the player the spider shouldn't be able to hit the play

What actually happened was...:
While planning out a new build I placed a platform to level out the land. An aggravated spider had gotten underneath and was able to hit me through the blocks

Steps to Reproduce:
1. Started a new creative world
2. Dug a pit and covered the top layer
3. Spawned spiders and aggravated them (they still hit the player)