To reproduce:
1. Open attached Unity project "ParticleScaleBug.zip"
2. Open "test" scene
3. In the Hierarchy, click on Particle System
4. In the Inspector, check "Bounds" to see the bounds of the particle system
5. Inspect the particle system in the scene view

Expected result: Particles should always stay in their bounds
Actual result: Particles reach further than the bounds if the coordinates are non-uniform (see attached gif "bounds.gif")

Reproduced on: 5.6.4p4, 2017.1.2p4, 2017.2.1f1, 2017.3.0f2, 2018.1.0a7