It is happening on our Standard Assets -> Particles -> Fireworks

Can't reproduce on 5.5.0p3
Reproduces on 5.6 only - !regression! not happening in 5.6.0a4 and a5, but happens in 5.6.0a6 and b1, b2, b3

How we can reproduce it using the example you attached
1 Create new project
2 Import StandardAssets package (https://www.assetstore.unity3d.com/en/#!/content/32351) from AssetStore
(or just open attached project)
3 Open scene "Particles"
4 Press Play
5 By clicking "Left" or "Right" sign select Fireworks particle
6 Wait for "launching fireworks"

Actual results: lot of errors appears in Console:
"Assertion failed on expression: 'particles.array_size() == count'"
"Assertion failed on expression: 'count == particles.array_size()'"
"Assertion failed on expression: 'count >= toIndex'"