Vista - Problem with WMI User Logoff

I am having a problem with the WMI User Logoff command.
It always forces a logoff, even when I'm not using that option.
I want my vbscript logoff to work the same as when a user selects "Logoff"
from the start menu.
i.e.
If you select "Logoff" from the Start menu, and you have not saved a
document, Word prompts you to save it.
If you don't respond to the "Save" dialog, an "End Program" dialog is
displayed.

I want to duplicate this behaviour.
Unfortunately, the Logoff command in WMI forces the logoff, and any unsaved
data is lost.
Here is the code I'm using. . .

Const cLogoff = 0
Const cShutdown = 1
Const cReboot = 2
Const cForceLogoff = 4
Const cForceShutdown = 5
Const cForceReboot = 6
Const cPowerOff = 8
Const cForcePowerOff = 12

Dim objWMI
Dim objComputer
Dim iRC

Set objWMI = GetObject("Winmgmts:{impersonationLevel=impersonate}")
For Each objComputer In objWMI.InstancesOf("Win32_OperatingSystem")
iRC = objComputer.Win32Shutdown(cLogoff,0)
Next

Any suggestions????