I've posted this to http://answers.microsoft.com/en-us/windows/forum/windows8_1_pr-files/windows-8-issue-with-drive-mapping-and-uac-enabled/2d1caf8c-31f5-4143-ae64-68796955751e but I was asked to repost it here.

I know it's a "security" issue, and I've seen it rehashed in other places, but Windows 8 breaks the EnableLinkedConnections registry patch in an interesting way.

Consider the following: Windows 8.1, Build 9431 (Though I've confirmed the issue exists in Windows 8 RTM)

Do a fresh install - Vanilla Settings. No customization except for the Computer Name.

1) "Disable" UAC by going into User Account Control settings and dragging the slider to the bottom. (I'm aware this doesn't completely disable UAC. Completely disabling UAC in the registry kills the App ecosystem, which is something I'm hoping to avoid)

2) Enable Linked Connections by creating a DWORD named EnableLinkedConnections with a value of 1 in HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System

3) Reboot the computer.

4) Open a command prompt and map H: to something (If you don't have a network in your test environment, map it to \\localhost\c$\windows) - net use h: \\localhost\c$\windows

5) In the same command prompt, change to H:, and do a DIR and see the contents of the folder as expected. (In my example, I get the contents of c:\windows)

6) Open a command prompt, but this time, Open as Administrator.

7) Run a "net use" and verify that the drive mapping is there. (Should see H: mapped)

8) Change to H: do a DIR and see that the contents are actually the root folder of the drive mapping. (In my example, dir h: lists everything in c:\ and not c:\windows)

9) Figuring this was a minor glitch, I decided to map the H: drive as administrator. (In the command prompt, net use h: /delete, then net use h: \\localhost\c$\windows - awesome. Now dir h: in the admin prompt works. Then, I go back to the non admin prompt and dir h: gives me a listing of the root directory again!

This is completely broken! There are many applications that need drive letter access to be consistent between security contexts from a "Run as Administrator" standpoint. This USED to work in Windows Vista and 7.

I know that turning off UAC using the registry (EnableLUA to 0) fixes this, but what's the point of Windows 8 if all the apps tell me that they won't run under the admin account? It just becomes an ugly version of Windows 7 with a bunch of non-functional icons.

I also realize that I could completely disable "EnableLinkedConnections" and double-map each drive, but that's a pretty crappy workaround to accomplish something simple that's always just worked. I get that it could make the system more vulnerable, but it's Opt-In. I have to turn off UAC, I have to create a registry key, so it's not something I've done accidentally.

Thank you for the detailed evaluation and explanation.

I have seen some Windows Networking oddities, in addition to some behavior I can only describe as "halting" (i.e., operations that should complete immediately take longer than expected, as though there has been some kind of error that must be retried).  I have not been evaluating the Windows 8.1 networking changes as specifically as you have, but have more been using network connections to get things set up for other evaluations.

It's possible what you're describing could be related to some of the glitches I've seen with Windows 8.1's "Windows Networking", as it may be trying to find files from places where the underlying path has been inadvertently changed (and the operations are thus failing and falling back to another layer).  I'll look further into the behavior changes with and without the EnableLinkedConnections tweak now.