Curved shadow on flat surface?

I was playing with shadows after seeing knacki’s post about contact shadows, and noticed that my shadow seemed curved on a flat plane (and moved on the plane as I shifted my camera).

I turned on wireframe to compare, and it seems like it’s definitely curved and shifting as I move my camera.

Is this a bug, or just an artifact of the way shadows are calculated?

Can you drag n drop your file in the web demo to see if you replicate the issue nomad - WebAssembly

Make sure to use perspective camera to see if the bug occurs.

The problem doesn’t appear to be present in the WebAssembly version: