the Microsoft of now obviously knows of the existence of these shell enhancements, but clearly doesn’t test patches against them at all

Microsoft taking into account this method of modding explorer in its testing would be like asking Apple's design team to take into account the one in a million iPhone user who sticks their phone up their butt. [0] I don't know what it says about Windows or its users that there must be more than one in a million people running this stuff, but still.

[0] https://www.youtube.com/watch?v=bsbpFKDIaZ0