While in a mineshaft a creeper had spawned and ran towards me, there was floating gravel naturally generated above me and in between the creeper and I. The line of sight was not blocked but the creeper would lose aggression as if the gravel was an invisible wall. There was a rail under the gravel and between the creeper and I. A player is able to fit underneath the gravel.

What I expected to happen was...:

The creeper should chase the player even under floating gravel.

What actually happened was...:
The creeper gets confused and tries to turn around

Steps to Reproduce:
1. Find floating gravel above a rail (unsure if rail has an affect)
2. Attempt to lead a creeper past the gravel and rail
3. Break the gravel and the creeper will see you again.

Attachment: Cobblestone = Gravel     Bat = Creeper