System Information
Operating system: Windows 10 64-bit
Graphics card: Geforce GTX 270

Blender Version
Broken: 2.80 e7a0f0a9934e
Worked: (optional)

Short description of error
The UV modifier and operator corrupts the UVs of models. Here is an image showing the problem:

First model is the raw, unwrapped basemesh I want to bevel, second is what it looks like after I add a bevel modifier, third is the desired result (manually fixed).

Exact steps for others to reproduce the error
Here's a blendfile with the three models from above:

Just apply any tiling texture with strong vertical lines and you'll be able to see the issue clearly.