Group policy drive mapping extension not applying to Vista SP2 machine

I have one GPO (called Desktop_User) that applies to a Windows 7 and a Windows Vista machine. When I log on to this systems, the drive mapping works on the Windows 7 machine but the Windows Vista machine (using the same AD account).

I just can't figure out what the cause may be. As the title says the Vista machine has the SP2 installed and therefor should already have the CSE for drive mapping installed (I have double-checked that it's installed by looking at HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\GPExtensions\{5794DAFD-BE60-433f-88A2-1A31939AC01F}. Disabling UAC via GPO didn't make a change.

Here is the trace found on the Vista client when Configure Drive Maps preference logging and tracingis activated. I don't see anything suspicious... any ideas?

2015-03-13 11:11:02.525 [pid=0x4f0,tid=0xc30] Entering ProcessGroupPolicyExDrives()
2015-03-13 11:11:02.541 [pid=0x4f0,tid=0xdbc] SOFTWARE\Policies\Microsoft\Windows\Group Policy\{5794DAFD-BE60-433f-88A2-1A31939AC01F}
2015-03-13 11:11:02.541 [pid=0x4f0,tid=0xdbc] BackgroundPriorityLevel ( 0 )
2015-03-13 11:11:02.541 [pid=0x4f0,tid=0xdbc] DisableRSoP ( 0 )
2015-03-13 11:11:02.541 [pid=0x4f0,tid=0xdbc] LogLevel ( 2 )
2015-03-13 11:11:02.541 [pid=0x4f0,tid=0xdbc] Command subsystem initialized. [SUCCEEDED(S_FALSE)]
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] ----- Parameters
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] CSE GUID : {5794DAFD-BE60-433f-88A2-1A31939AC01F}
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] Flags : (   ) GPO_INFO_FLAG_MACHINE - Apply machine policy rather than user policy
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc]         (   ) GPO_INFO_FLAG_BACKGROUND - Background refresh of policy (ok to do slow stuff)
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc]         (   ) GPO_INFO_FLAG_SLOWLINK - Policy is being applied across a slow link
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc]         (   ) GPO_INFO_FLAG_VERBOSE - Verbose output to the eventlog
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc]         (   ) GPO_INFO_FLAG_NOCHANGES - No changes were detected to the Group Policy Objects
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc]         (   ) GPO_INFO_FLAG_LINKTRANSITION - A change in link speed was detected between previous policy application and current policy application
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc]         (   ) GPO_INFO_FLAG_LOGRSOP_TRANSITION - A change in RSoP logging was detected between the application of the previous policy and the application of the current policy.
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc]         ( X ) GPO_INFO_FLAG_FORCED_REFRESH - Forced Refresh is being applied. redo policies.
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc]         (   ) GPO_INFO_FLAG_SAFEMODE_BOOT - windows safe mode boot flag
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc]         (   ) GPO_INFO_FLAG_ASYNC_FOREGROUND - Asynchronous foreground refresh of policy
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] Token (computer or user SID): S-x-x-xx-xxxxxxxxxx-xxxxxxxxxx-xxxxxxxxxx-xxxxx
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] Abort Flag : Yes (0x0049e960)
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] HKey Root : Yes (0x000003f4)
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] Deleted GPO List : No
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] Changed GPO List : Yes
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] Asynchronous Processing : Yes
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] Status Callback : Yes (0x745dd375)
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] WMI namespace : Yes (0x0236ad7c)
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] RSoP Status : Yes (0x0147fd2c)
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] Planning Mode Site : (none)
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] Computer Target : No (0x00000000)
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] User Target : No (0x00000000)
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] Calculated list relevance. [SUCCEEDED(S_FALSE)]
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] ----- Changed - 0
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] Options : (   ) GPO_FLAG_DISABLE - This GPO is disabled.
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc]           (   ) GPO_FLAG_FORCE - Do not override the settings in this GPO with settings in a subsequent GPO.
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] Options (raw) : 0x00000000
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] Version : 1310740 (0x00140014)
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] GPC : LDAP://CN=User,cn={BB9C459F-007E-41BF-A21A-31BD45B831AE},cn=policies,cn=system,DC=testad,DC=contoso,DC=com
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] GPT : \\testad.contoso.com\SysVol\testad.contoso.com\Policies\{BB9C459F-007E-41BF-A21A-31BD45B831AE}\User
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] GPO Display Name : Users_Desktop
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] GPO Name : {BB9C459F-007E-41BF-A21A-31BD45B831AE}
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] GPO Link : (   ) GPLinkUnknown - No link information is available.
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc]            (   ) GPLinkMachine - The GPO is linked to a computer (local or remote).
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc]            (   ) GPLinkSite - The GPO is linked to a site.
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc]            (   ) GPLinkDomain - The GPO is linked to a domain.
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc]            ( X ) GPLinkOrganizationalUnit - The GPO is linked to an organizational unit.
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc]            (   ) GP Link Error
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] lParam : 0x00000000
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] Prev GPO : No
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] Next GPO : No
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] Extensions : [{00000000-0000-0000-0000-000000000000}{2EA1A81B-48E5-45E9-8BB7-A6E3AC170006}][{25537BA6-77A8-11D2-9B6C-0000F8080861}{88E729D6-BDC1-11D1-BD2A-00C04FB9603F}][{42B5FAAE-6536-11D2-AE5A-0000F87571E3}{40B66650-4972-11D1-A7CA-0000F87571E3}][{5794DAFD-BE60-433F-88A2-1A31939AC01F}{2EA1A81B-48E5-45E9-8BB7-A6E3AC170006}]
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] lParam2 : 0x004a78bc
2015-03-13 11:11:02.556 [pid=0x4f0,tid=0xdbc] Link : LDAP://OU=Users,DC=testad,DC=contoso,DC=com
2015-03-13 11:11:02.587 [pid=0x4f0,tid=0xdbc] Read GPE XML data file (2510 bytes total).
2015-03-13 11:11:02.603 [pid=0x4f0,tid=0xdbc] Starting filter [AND NOT FilterGroup].
2015-03-13 11:11:02.619 [pid=0x4f0,tid=0xdbc] Starting filter [AND FilterGroup].
2015-03-13 11:11:02.619 [pid=0x4f0,tid=0xdbc] Starting filter [AND NOT FilterGroup].
2015-03-13 11:11:02.619 [pid=0x4f0,tid=0xdbc] Completed get next GPO. [SUCCEEDED(S_FALSE)]
2015-03-13 11:11:02.619 [pid=0x4f0,tid=0xdbc] WQL : SELECT * FROM RSOP_PolmkrSetting WHERE polmkrBaseCseGuid = "{5794DAFD-BE60-433f-88A2-1A31939AC01F}"
2015-03-13 11:11:02.650 [pid=0x4f0,tid=0xdbc] Purged 4 old RSoP entries.
2015-03-13 11:11:02.650 [pid=0x4f0,tid=0xdbc] Logging 4 new RSoP entries.
2015-03-13 11:11:02.650 [pid=0x4f0,tid=0xdbc] RSoP Entry 0
2015-03-13 11:11:02.665 [pid=0x4f0,tid=0xdbc] RSoP Entry 1
2015-03-13 11:11:02.665 [pid=0x4f0,tid=0xdbc] RSoP Entry 2
2015-03-13 11:11:02.665 [pid=0x4f0,tid=0xdbc] RSoP Entry 3
2015-03-13 11:11:02.681 [pid=0x4f0,tid=0xdbc] Completed get GPO list. [SUCCEEDED(S_FALSE)]
2015-03-13 11:11:02.697 [pid=0x4f0,tid=0xc30] Leaving ProcessGroupPolicyExDrives() returned 0x00000000

[Edit]

I have tried to follow this guide here and enforce the installation of KB943729, but it doesn't make a change.

It turned out I had to configure the following settings... now it's working smoothly...

User Account Control: Behavior of the elevation prompt for administrators in Admin Approval Mode 
==> Elevate without prompting 
User Account Control: Detect application installations and prompt for elevation 
==> Disabled 
User Account Control: Only elevate UIAccess applications that are installed in secure locations 
==> Disabled 
User Account Control: Run all administrators in Admin Approval Mode 
==> Disabled 
Always wait for the network at computer startup and logon 
==> Enabled 

You should also consider setting the following registry key as supposed on TechNet :

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System\EnableLinkedConnections = 1 (DWORD)