System Information
Operating system: Linux-5.3.0-45-generic-x86_64-with-debian-buster-sid 64 Bits
Graphics card: GeForce 9800 GT/PCIe/SSE2 NVIDIA Corporation 3.3.0 NVIDIA 340.107

Blender Version
Broken: version: 2.82 (sub 7), branch: master, commit date: 2020-02-12 16:20, hash: rB77d23b0bd76f
Worked: (optional)

Short description of error
When you add several materials with textures, the mesh breaks and you cannot continue working in texture mode.

Exact steps for others to reproduce the error
Use the texture type view, in flat mode with shadows activated
the initial cube modifies its geometry
add 1 texture to the material
Create a new material and add it to some parts of the mesh.
When you do this you will see the bug,
This also happens when you simply add more materials to a mesh.
 

[Based on the default startup or an attached .blend file (as simple as possible)]