How to reproduce:

1. Open a new project
2. Import attached package
3. Select the Particle System gameobject in the scene view
- A plane should become visible in both the scene and game views
4. Play the scene
- Note how the cube with the rigidbody falls and lands on the plane
- Deselecting the particle system causes the plane to disappear and the cube falls through
- If the Visualisation mode for the plane is Grid (instead of Solid), no collision happens either

- Reproduced in 5.6.0a6 (af2099d5a7ac), 5.6.0b3 (358ff4ed3952), 5.5.0f3 (1d1a0b50d15c)