Windows Defender isnt cleaned under Vista. In the WinApp.ini the entry appears as:

[Windows Defender]
LangSecRef=3024
Detect=HKLM\SOFTWARE\Microsoft\Windows Defender
Default=True
FileKey1=%commonappdata%\Microsoft\Windows Defender\Scans\History\Results\Quick|*.*
FileKey2=%commonappdata%\Microsoft\Windows Defender\Scans\History\Results\Resource|*.*

The problem is that %commonappdata% is not supported under Vista. The correct paths are:
FileKey1=C:\ProgramData\Microsoft\Windows Defender\Scans\History\Results\Quick|*.*
FileKey2=C:\ProgramData\Microsoft\Windows Defender\Scans\History\Results\Resource|*.*