To reproduce:
1. Open attached project
2. In Project window, select TestParticleSystem
3. In Inspector window->Particle System component->Emission module, change Rate over Distance to any value
4. In main menu toolbar, press ReadRateOverDistance->ReadRateOverDistance
5. Observe Rate over Distance Debug Logging the parameter's value

Expected: value doesn't change
Actual: value is reset to zero when Debug.Log() is executed to print out the parameter (check .gif attached)

Reproduced in: 2017.3.0a6, 2017.3.1p4, 2018.1.0b11, 2018.2.0a5
Not reproduced in: 2017.1.3p2, 2017.2.2p1, 2017.3.0a5

Note: fraction of script used to load Assets while in edit mode:
ParticleSystem ps = AssetDatabase.LoadAssetAtPath<GameObject>("Assets/TestParticleSystem.prefab").GetComponent<ParticleSystem>();
Debug.Log(ps.emission.rateOverDistance.constant);