Why does Blender "click through" my mesh?

https://imgur.com/ktdeqjk

Blender seems to be getting the ray trace completely wrong here and ignoring/"clipping through" the mesh. I’m pressing CTRL + RMB to create a new vertex but I’ve noticed this problem occurs with other operations too; the 3D cursor works fine however.

I only installed Blender the other day – don’t think I’ve fiddled with any relevant settings.

I have an AMD CPU.