Steps to reproduce:

1. Open attached project "779420.zip"
2. Open scene "test"
3. In Player settings set rendering path to forward
4. Run scene
5. In project tab, select "Test" render texture and notice that it shows view from two cameras separately
6. Stop scene
7. In Player settings set rendering path to deferred
8. Run scene
9. In project tab, select "Test" render texture and notice that this time only one camera's view is shown which is stretched on whole texture

Reproduced with: 5.2.4f1, 5.3.4f1, 5.4.0b10