My Thinkpad X61T dockec in Ultradock does the same when I have Thinkpad USB keyboard attached. There are times it does not fire up from sleep, but to ensure that it stays in sleep, I typically remove the USB keyboard before putting it to sleep.
But, given your scenario of disabling wake up with mouse and keyboard there could be other ways the machine is woken up. You might want to list out what you have attached.
Sometimes the network adapters can also play into it and wake up the OS from sleep.
The surest way to ensure it does not come up is disconnect & disable most connections and peripherals and see if that prevents this from happening.
Also, they can be attached/ removed via a process of elimination to go through the peripherals.
That's how I figured out it was my keyboard causing it.
PS: Maybe one of your forefathers has found this as a medium to garner your attention :)
Pointing out some examples of peripherals that have their power issues.