How do One Way Wall-bangs in CSGO work?

I don't know of any current one-way wallbangs, but generally they are considered bugs, and if I recall correctly, have been fixed in the past.

As to why they occur: - The Source engine calculates damage modifiers per-angle and direction - This means that you might actually be getting bullets through on one side but not the other - I'm going to go out on a limb and say these are difficult to test without a large sample audience