System Information:
Operating system: Linux
Graphics card: GTX 1050ti 440.64

Blender Version:
Broken: 2.90 (13abd3784ad0), 2.83 (d0d16eb7d347), 2.82a Release, potentially older versions
Worked: Unsure

Short description of error:
Viewport shading shadows will invert if viewed through a culled backface. Here's an example video:

I'm unsure if it is the same issue as T76084 so I've split it off to this different report. I understand the two issues may be the same one manifesting in different ways. If this is the case, just say so, merge the cases, and I'll update the description of the original to include this information.
I have seen this issue occur in a personal project (take note of the shadow around the Window, ignore the red note):

Exact steps for others to reproduce the error:
Use this .blend file or follow the steps below.

1. Create a scene where an object is casting a shadow onto another one while the "Viewport shading>Shadows" option is enabled.
2. Create an object where you can see it's backface and place it so the objects backface obscures your view of the shadow cast by the object in the first step.
3. Enable "backface calling" in the viewport shading options and notice that the shadows behind the backface are inverted from what's expected.