This impacts enclosed rooms, walls, houses, and virtually any player build. A tunnel is just the easiest way to demonstrate that it is truly completely broken. 

Steps to Reproduce:
1. Allow a mob to begin tracking you in survival mode.
2. Enter one side of a completely enclosed tunnel, and block yourself in there.
3. Run to the other side of the tunnel.
Observed Results:
The mob follows you to the other side of the enclosed tunnel, regardless of its material (solid, transparent, etc.)
Expected Results:
The mob's pathfinding is broken off once inside of a tunnel.