System Information
Operating system: Windows-7-6.1.7601-SP1 64 Bits
Graphics card: Quadro FX 3800/PCIe/SSE2 NVIDIA Corporation 3.3.0

Blender Version
Broken: version: 2.81 (sub 16), branch: master, commit date: 2019-12-04 11:32, hash: rBf1aa4d18d49d
Worked: (optional)

Short description of error
In both 2.81 and 2.81a using more than one material causes the faces assigned material #2 or more to disappear. This problem does not occur in 2.80.

Exact steps for others to reproduce the error

Add a default sphere
Assign a material
Create a second material
In Edit Mode assign the new material to the selected faces
All the faces with the newly assigned second material disappear
Same happens with a third material