How to reproduce:
1. Open attached project "Particle_Bounds_Bug.zip" and scene "BoundsTest"
2. In Hierarchy window, select "Emit Cylinder"
3. In Scene view -> Particle Effect -> enable "Show Bounds"
4. Observe Scene/Game views

Expected result: the bounds of the particle system is large enough to enclose all the particles
Actual result: the bounds are too small if the mesh is too long

Reproducible with: 2017.1.3p4, 2017.2.3f1, 2017.4.3f1, 2018.1.1f1, 2018.2.0b4

Notes:
- In order to notice particles going out of the bounds set "Emit Cylinder" -> "Particle System" component -> "Renderer" -> "Render Alignment" -> "World"
- 2017.4 and below the bounds are in square shape (particles go out of bounds less, but overall the bounds are too large)