Thanks for the report. My experience has been very similar. I think your evidence suggests that it isn't a power issue but a MS firmware issue. Annoyingly, my OP got stuck into this chain which is considered "Answered" so
I'm not sure MS people look at it again. This is very frustrating since I'm worried that this glitch like the one I posted about the problem with Daisy chaining Dell monitors won't get fixed.
OK waverlybrian -- Success! I have my hardware-encrypted drive working now by "manually" changing the power state from D3 (deepest sleep state -- the default for Surface Pro 3 USB drives) to D0 (always on). Since I use the dock,
there is no need to conserve power and I should have been able to turnoff power saving in the device manager, but the check box there for selective suspend does NOT function. Others on the web say there is a flaw in the user interface so it does not change
the required key value if the key does not yet exist for the device, so the default of D3 never changes unless you go into the registry and create the key. I didn't really want to meddle with the registry by hand so finally tried out a powershell script that
a MSFT person posted. An update at the top of the post says the powershell script workaround should no longer be required because a Windows update mid 2014 fixed this and other USB issues. But looks like the "fix" did not take for my system. The powershell
script did. You can try it (your own risk, but probably a small one!) by reading the post at:
http://blogs.msdn.com/b/usbcoreblog/archive/2013/11/01/help-after-installing-windows-8-1-my-usb-drive-disappears-or-file-transfers-stop-unexpectedly-r-a-post-title.aspx
Read this section near the bottom of the post:
PowerShell script to disable suspend
I download the script and ran ToggleSuspend.ps from an administrative command window. It only works on drives that are currently plugged in, and mine only stayed plugged in for 30s, so
I had mount it quickly, then run the script quickly so it could see the drive and write the registry key for it.
It worked (drive stayed on past 30 s) on reboot, changing the D3 power state that used to be there (deepest sleep) to D0 (always on).
Now in device manager the Buffalo drive shows the correct D0 state (look for Power data in the dropdown list). You should uncheck the power settings on the USB Root Hub to which your external hard drive is connected since power management is supposed
to be able to selectively suspend the hub itself as well as specific devices on it (go to its Power Management tab).
Hope this works for you and for others who have trouble with devices disconnecting too often. All my other USB drives are OK (they get suspended at about 30s, but come awake quickly and without issue). I really needed the fix for the encrypted one which
locks itself when going to sleep.