To reproduce:
1. Open attached project;
2. Open "Scene" scene;
3. Click on the "FrontCamera" and set the Viewport to (0;0;1;1)
-notice the Depth is set to 2;
4. Click on the "MidleCamera" and set the Viewport other than (0;0;1;1)
-notice the Depth is set to 1.

Expected result: the Sphere should be in front of the Cube.
Actual result: the Cube is in front of the Sphere unless both cameras Viewport is set to (0;0;1;1).

Reproduced on versions: 5.6.0b1, 5.6.0b9, 2017.1.0a2.
Not reproduced on version: 5.5.2p1.
Regression found in version: 5.6.0b1.