Reproduction steps (Cinemachine 2.2.0+):
1. Open attached project ("RandomCamera")
2. Create Instance of any single Cinemachine Camera(not a child and not a parent)
3. Make 100+ duplicates of the original Cinemachine Camera
4. Select any duplicate in Hierarchy window and enter and quit Playmode
5. Notice that majority but some Cameras have their setting changed

Reproduced in:
With Cinemachine 2.1.10: 2017.2.3p2, 2017.4.7f1, 2018.1.9f1, 2018.2.0f2, 2018.3.0a4
With Cinemachine 2.2.0 and 2.2.6: 2018.2.0b1, 2018.2.0f2, 2018.3.0a4

Notes:
- Cinemachine 2.1.10 has repro only when duplicating child cameras
- Cinemachine 2.2.0 and 2.2.6 has repro when duplicating all Child cameras, and when duplicating single cameras by steps written above