Not a bug but more an incorrect assumptions by ImageMagick:
Warning: Found more than one ImageMagick installation. This could cause problems at runtime.
/usr/bin/Magick-config reports version 6.9.4 Q16 is installed in /usr
/usr/bin//Magick-config reports version 6.9.4 Q16 is installed in /usr
Obviously, ImageMagick assumes that "/" is different to "//".
I have no idea why two "/" appear but either way, the ImageMagick script should
ignore more than one "/" following in succession, for determining whether another
installation exists (there actually does exist one, but it is at /Programs/Imagemagick/6.9.4",
don't ask me why the script checks for the same path there though as it is identical)