System Information
GPU: GeForce GTX 970
CPU: Intel(R) Core(TM) i5-2550K CPU @ 3.40GHz
Memory: 16 GB RAM (15.95 GB RAM usable)
Current resolution: 1920 x 1080, 60Hz
Operating system: Microsoft Windows 10 Pro

Blender Version
Broken: blender 2.79.6 72b1fb99344
Worked: At least 2.79b

Short description of error
At some point in Sculpt Mode mask just disappeared visually. It's still there, I can't move masked areas, but it's also invisible. Have no idea how that happened. New objects in the same scene have the same issue. In new scene works fine. On a screenshot you can see how same scene looks in 72b1fb99344 at the top and 2.79b at the bottom.

Exact steps for others to reproduce the error
Just open this scene and switch to sculpt mode.