Repro:
1. Open QA attached project "repro"
2. Enter Play Mode
3. Click and hover the mouse over both cubes
4. Exit Play Mode
5. Build and run the game: File -> Build and Run
6. Repeat step 3 and observe

Expected: each Cube gets rotated and its color changed when hovering and clicking on it both in Play Mode and in the build
Actual: the Cube on the left neither gets rotated nor changes its color when hovering and clicking on it in the build

Reproducible with: 2018.2.a6, 2018.2.0b1
Not reproducible with: 2017.1.3p3, 2017.2.2p3, 2017.4.1f1, 2018.1.0f1

Notes: Only the view rendered by a camera which has the highest depth triggers mouse events. This goes for all of the OnMouse events: OnMouseDown, OnMouseDrag, OnMouseEnter, OnMouseExit, OnMouseOver, OnMouseUp, OnMouseUpAsButton.

Fixed in: 2018.3.0a9
Backported to: 2017.4.11f1