To reproduce:
1. Open the "bugreport" scene in the attached project
2. Double-click "Example-Mask-Problem-FIX" Game Object from Hierarchy
3. Move camera in front of it in the Scene view
4. Observe the image at the right side

Desired outcome: Image at the right side has its overlapping distortions blended smoothly when moving the camera around.
Actual result: Image at the right side displays distortion edge depending on the camera position.

Reproduced with 5.4.0b1, 5.4.5p4, 5.5.4p1, 5.6.2p1, 2017.1.0f1, 2017.2.0b1
Not reproduced with 5.3.3f1, 5.3.8f2, 5.4.0a4
Regression introduced between versions 5.4.0a4 and 5.4.0b1