JaguarFiendThere is actually something you can for me if you haven't done this already. Detail exactly what you did with your HUD or whatever you did to give you those enormous square cheater shadows and give this information to someone trustworthy (I nominate Nursey). Then we can send this to Valve with an explanation and maybe some time in the next year and a half if we're lucky it might get addressed and fixed.
Oh there was a whole thread about that.
JarateKing was able to figure out how it works.
https://www.teamfortress.tv/50818/square-shadows
edit: To address how it happened. I never made the additions to the HUD that made the shadows happen. The hud is made by arekk and I found the download link on Nursey's stream.