UAC plugin CallFunctionAsUser GetTempPath returns empty?

I want to make an installer with UAC plugin where I can detect some original user folders using the user level process, and then copying files to Program Files using the elevated admin user process.

I began by finding the TEMP folder, calling GetTempPath using System plugin, but calling it in the user level process returns emtpy string or "0" ("0" if I run it in a virtual XP from a non-admin user, and when the elevation dialog pops I enter an admin user credentials).

Can anybody tell me why it happens or how should I do it? Here's my complete script:

SetCompressor lzma
OutFile .\TempDir.exe
Name "TempDir"
VIProductVersion "1.0.0.0"
VIAddVersionKey "FileVersion" "1.0.0.0"
VIAddVersionKey "FileDescription" "TempDir"
VIAddVersionKey "ProductName" "TempDir"
VIAddVersionKey "CompanyName" "Temp dir Inc."
VIAddVersionKey "LegalCopyright" "lalala (c) 2009"
RequestExecutionLevel user
SilentInstall silent
!include UAC.nsh
!include LogicLib.nsh
Function .OnInit
    ${UAC.I.Elevate.AdminOnly}
FunctionEnd
Function .OnInstFailed
    ${UAC.Unload}
FunctionEnd
Function .OnInstSuccess
    ${UAC.Unload}
FunctionEnd
!define GetTemp "!insertmacro GetTemp"
!macro GetTemp Answer
    Call GetTemp
    Pop ${Answer}
!macroend
!define UserGetTemp "!insertmacro UserGetTemp"
!macro UserGetTemp Answer
    ${UAC.CallFunctionAsUser} GetTemp
    Pop ${Answer}
!macroend
Function GetTemp
    Push $R1
    
    Push $R0
    System::Call "*(&t${NSIS_MAX_STRLEN}) i .R0"
    System::Call "kernel32.dll::GetTempPathA(i ${NSIS_MAX_STRLEN}, i R0)"
    System::Call "*$R0(&t${NSIS_MAX_STRLEN} .R1)"
    System::Free $R0
    Pop $R0
    
    Push $R2
    StrCpy $R2 $R1 "" -1
    ${If} $R2 == "\"
    ${OrIf} $R2 == "/"
        StrCpy $R1 $R1 -1
    ${EndIf}
    Pop $R2
    
    Exch $R1
FunctionEnd
Section
    ${UserGetTemp} $0
    ${GetTemp} $1
    MessageBox MB_OK "$$TEMP: $TEMP$\nUser Temp: $0$\nTemp: $1"
SectionEnd

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