count me in as well with my SP2.
But, using "powercfg -devicequery wake_armed" may have found a solution. it listed the following as candidates:
HID-compliant mouse
HID-compliant mouse (001)
Surface Type Cover Filter Device
HID Keyboard Device (001)
Going into the Device Manager, Power Management tab for each device and deselecting "Allow this device to wake the computer" seems to have solved preventing it going to sleep
. I tried differing combinations of having some of these on and some off and for me, it only works if they are all unchecked. So it looks like the Type Cover drivers are to blame. What's odd is even if the cover isn't connected it still won't sleep without these power setting adjustments.
Hope this helps someone else.