Reproduction steps:
1. Open unitypackage attached (20170318_bugreport_ParticleSystem_3D_startRotation.unitypackage).
2. Open scene "bugreport_ParticleSystem_3D_startRotation".
3. Press play.
4. Inspect current particle rotation.
5. Select Particle system.

Expected result: Particle rotation will remain MinMax between 2 values on X and Y axis.
Actual result: Particle rotation only use only biggest MinMax values.

Note: It works correctly if you do not select Particle System during Play mode or if all 3 values are assigned. If you change 2 or 1, selecting particle system will trigger this issue.

Reproduced on: 5.5.0f3, 5.6.0f2, 2017.1.0a5.