It's definitely not standard USB. Yes, they show up as USB devices, but on GNU/Linux at least you can clearly see it's all under the same "composite USB device" (which houses the wacom, sensors, etc. If the cover is attached, it appears as interface 3 of this device).
Also unplugging/plugging does not make any USB device appear/disappear; rather, this "composite" device briefly resets.
Curious, are you dual-booting Win8.1/Linux on an SP2?
I've been using Hyper-V for Linux and FreeBSD, but of course inside a VM the host's drivers aren't visible. Running these OS in VM is very handy for many tasks, and seems easier to set up than the dual-booting alternative.