When you have in the scene deferred camera with lowest depth, other cameras clears deferred camera depth buffer (even with Clear Flags = Dont't Clear).

In "TwoCameras" scene contains few objects: "Cubes", "Occluded Sphere", "Foreground Sphere", one of them is occluded by boxes (In scene view),
but as you should notice it is not occluded in game view.
- "Occluded Sphere" and "Foreground Sphere" rendered with forward camera, Clear Flags = Dont't Clear, Depth = 0.
- "Cubes" rendered with Deferred Camera, Clear Flags = Skybox, Depth = 1.

1. Open project.
2. Open scene "TwoCameras".
3. You should notice that "Occluded Sphere" is not occluded by the cubes in game view.
4. Select "Deferred Camera".
1. Disable "Depth Of Field" script.
2. Set Rendering Path = Forward.
5. Now, "Occluded Sphere" object is occluded as it should be in game view.
6. Select "Deferred Camera".
Set Rendering Path = Deferred.
7. Play scene and problem should appear again.
(Only after playing the scene, game view updates, so it may be another bug. It's really hard to find the source of the problem, but
something is definitely not right with deferred cameras.)

Reproduced: 5.0.0b18, 5.0.0b14, 4.6.f1