I have reported this already about 8 months ago while being in the insider program over the Microsoft feedback tools, so I am very pleased that this bug still is present in the final version...
The problem is simple, Dell Venue 8 Pro shows this problem. I also have found reports about this on other forums by Lenovo and Asus, so I think it's a problem with the Intel BayTrail or DPTF drivers.
The problem is simple:
1.) Let Windows idle
2.) Open TaskManager (or for example CPUz) and monitor CPU throttling
Under Windows 10, the CPU throttling seems to be broken for at least Intel Atom BayTrail (3700 series). The CPU always stays around 1.3-1.7GHz @ 1-3% CPU load.
The same (normal) idle behavior under Windows 8.1 results in the processor correctly using the lowest energy states between 0.5-0.8GHz.
This results in a way noticeable faster battery drain.
2nd bug, mostly related: The battery drain in connected standby is about 3 times higher (~1.1mW/h), compared to Windows 8.1 (~0.33mW/h). The normal drain, by Microsoft itself, is 0.3mW/h for a device supporting connected standby mode.
Heres a video showing problem 1:
https://dl.dropboxusercontent.com/u/14937594/win10cpubug.mp4
You can see how the CPU throttling is not working properly always staying at mid-highe throttling state of the Atom CPU. Normal throttling would be 0.8GHz.
Here is how it should correctly be:
https://dl.dropboxusercontent.com/u/14937594/normal-idle-throttling.mp4
(sorry for the bad quality)
On my desktop PC and my Ultrabook the throttling work fine, so it seems a problem related to the Atom BayTrail drivers under Windows 10 or a combination of things.