Repro steps:

1. Open attached projects "cam_viewport_rect_depth_fail" scene
2. Set the view port of all the cameras to (0;0;1;1)
3. Set "Camera" Depth to 0, "Camera (1)" to 1, "Camera (2)" to 2
4. Change "Camera" view port to (-0.6;0;1;1)
5. Change "Camera (1)" view port to (0.6;0;1;1)
6. See that the "Camera (2)" depth is ignored

Expected: For the views to line up according to the depth

Actual: The two cameras that had the view port values changed are in from of the third camera even though it might be the nearest one

Reproduced with: 2017.1.0a6, 5.6.0f3(f2, f1)

Working with: 5.5.3f1, 5.4.0f3

Attached images(bad and good)