Spawners have strange face culling behavior

Spawners, when having blocks placed next to them, will have the opposite internal face culled. This appears to only affect the north and south faces, despite all faces of the model having similar cullface values.

How to reproduce

1. Place down a Spawner
2. Place a solid block either to the north or south of the Spawner
3. Observe as the opposite, inside face of the Spawner is culled