To reproduce:
1. Open attached project
2. Open scene03. It contains a few particle systems and a camera which is facing away from them and has some distance between itself and the particles
3. Enter play mode - notice how parts of the particles are still visible through the game view even though the particle systems are clearly outside the viewport

This seems to be related to the "Max particle size" in the "Renderer" part of the system. The documentation states that the valid values are 0-1, but in this case the value is 2