How to reproduce:
1. Open the attached project's Scene labeled "EditorMouseInput"
2. Enter the Play Mode
3. In the Game view, target the "Display 1"
4. Click on the Sphere
4. Inspect the behavior
5. In the Game View, target the "Display 2"
6. Click on the Sphere
7. Inspect the behavior

Expected result: OnMouseDown is called and the Sphere is colored blue
Actual result: OnMouseDown is not called on the Sphere shown on "Display 2"

Reproducible with: 2018.4.32f1, 2019.4.21f1, 2020.2.7f1, 2021.1.14f1, 2021.2.0b2, 2022.0a2

Important: OnMouseDown is called on Sphere shown in "Display 1" when clicking in "Display 2" if the click is relative to the displayed Sphere's position on "Display 1"

Note:
- Partially fixed in Unity 2021.1.0a8 and versions above. OnMouseDown is called on "Display 2" but when clicking on a specific point on "Display 2" it can be called on "Display 1" as well.