Steps to reproduce:

1) Download attached project '561f1.zip' and open in Unity
2) Open scene 'ParticleBatchIssue' and press Play
3) Enable Frame Debugger
You will see in the Frame Debugger that particles with mesh Render Mode and same material are rendered with 3 draw calls

Expected result: Particles with mesh Render Mode and same material should be rendered with 1 draw call (check attached image 'expected.png')
Actual result: Particles with mesh Render Mode and same material are rendered with 3 draw calls (check attached image 'actual.png')

Reproduced with:
5.5.4p3, 5.6.3f1, 2017.1.0p3, 2017.2.0b7, 2017.3.0a4

Note: all 3 particles are rendered with 1 draw call(check Frame Debugger) if Render Mode is Billboard