In shadowmask mode, particles that cast shadow and have Alpha Blended shader can affect mixed lights in the scene. It is possible to observe the bug when zooming in and out or when changing the shadow distance in Quality Settings.

Steps for reproduction:
1) Download the project below (ShadowCascadesSmallRepro) and open the scene `t2`
2) Find `ParticlesGymDustMotes` object in the hierarchy and select it (make sure to play the particle system and pause it)
3) While hovering the mouse on Scene view, press `F` key to focus on it
4) Focus on the cube in the scene view
5) Change shadow distance or zoom in and out the camera
6) Observe the bug

Notes:
- Regression from 5.6
- Issue also seems to be related to Near Clipping Plane of scene/game view camera
- Alpha Blended shader doesn't seem to be supported for shadowmasks
- Disabling particle renderer or shadow casting option resolves the issue
- Reproducible in both deferred and forward rendering paths
- A gif that demonstrates the problem is attached below