SubEmitter created in scaled-up particle system appears to not emit in Y or is not affected by speed.

Repro steps:
1. Open Particles scene from attached project.
2. Select SubEmitterBirth (SubEmitter of ParticleSystem) in the Hierarchy.
3. Preview in Scene view.
4. Observe how all particles are spawned at a flat disk.
5. Try changing the speed value. Observe how the emitter still remains flat.

Expected outcome: SubEmitter to work properly in 3 dimensions.

Notes:
- Managed to repro only once: used a scaled up particle system, then creates SubEmitter and it appeared as a flat disc (see image).
- Can't tell for sure if it's a regression. It only happened with 5.4.0b6, but saving the particle system out as a prefab and bringing it in an older version (5.3.1f1) still shows the error.
- Duplicating that SubEmitter or creating new ones fixes issue.
- Though particle system is white, colored dots appear on the edges.