Mobs will not pathfind across open trapdoors from the side

Steps to reproduce

See

1. Make a 9x9 platform with solid blocks, then place 4 blocks next to it with an air gap between each block and the platform and each other other block.

2. Place 4 trapdoors in the 4 gaps between each single block and the platform, with each trapdoor oriented in a different direction.

3. Open each trapdoor.

4. Spawn a mob on each of the 4 single solid blocks, and wait for them to wander toward the 9x9 platform.

Expected result

All 4 mobs try to wander to the larger solid platform.

Observed result.

2 of the 4 mobs try to wander to the larger solid platform. (They should fall through the open trapdoors, but they may not due to MCPE-181006.) Only the mobs that can attempt to cross an open trapdoor at its hinge or opposite its hinge do so. The mobs that should attempt to cross an open trapdoor at its sides never move.