Mob pathfinding considers the void to be a solid platform

When pathfinding, the mob AI does not take in to account the void as a fall.
To reproduce, lead a mob towards you by any method (shown with angry pigmans chasing the player), with a hole into the void intersecting their path. They should walk into the hole as though the void were a solid platform.

Tested using the 'flat' world type in creative mode, with mobs spawned via spawn eggs.