Reproduction steps:

1. Create a New Project
2. Create an "Animator Controller"
3. Create 3 "Animations"
4. Add those "Animations" to the created "Animator Controller"
5. Create 2 "Animator Override Controller"
6. Select both "Animator Override Controller"
7. Drag the created "Animator Controller" to the "Animator Override Controller" "Controller" field
8. Create 4 "Animations"
9. Add 3 of the 4 new "Animations" to the first "Animator Override Controller"
10. Select both of the "Animator Override Controller"
11. Add the 4th "Animation" to the first field in the "Animator Override Controller"
12. Select the second "Animator Override Controller"

Expected Result: Only the first field is populated by the 4th "Animation" that was added to both of the "Animator Override Controller"
Actual Result: The populated fields of the first "Animator Override Controller" copies over to the second "Animator Override Controller", not just the 4th "Animation"

Reproduced with: 2019.1.0a2, 2018.3.0b3, 2018.2.9f1, 2018.1.9f2, 2017.4.11f1

Note:
Selecting multiple "Animator Override Controller" which control the same "Animator Controller" and adding/changing any animation in any field, overrides all the other "Animator Override Controller" to the values of the currently edited "Animator Override Controller"