Help: Windows Installer 2.0 corrupts explorer.exe

When I install InstMsiA.exe (version 2.0.2600.2) the windows installer for
win98, it affects explorer.exe. When I right click a file to examine its
properties it copies the entire file into the temp directory displays the
properties sheet and then deletes the tempory file. You can only spot it
doing this if the file is a few hundred MB, so I can't be sure it's doing
this for small files, though if the file is really large (arround a GB) it
doesn't do it at all. I've been able to isolate the problem to msisip.dll.
Explorer.exe is version 4.72.3110.1. I run with most options turned off and
the following reg settings:

[HKEY_CURRENT_USER\Software\Microsoft\Windows\Curre ntVersion\Policies\System
]
"DisableTaskManager"=dword:00000001

[HKEY_CURRENT_USER\Software\Microsoft\Windows\Curre ntVersion\Policies\Explor
er]
"NoDriveTypeAutoRun"=hex:95,00,00,00
"NoFavoritesMenu"=dword:00000001
"NoRecentDocsMenu"=dword:00000001
"NoRecentDocsHistory"=dword:00000001
"NoStartBanner"=dword:00000001
"NoLogoff"=dword:00000001
"NoSetActiveDesktop"=dword:00000001
"NoFolderOptions"=dword:00000000
"NoActiveDesktop"=dword:00000001

[HKEY_LOCAL_MACHINE\Software\CLASSES\*\shell\openas \command]
@="C:\\WINDOWS\\rundll32.exe shell32.dll,OpenAs_RunDLL %1"

[HKEY_CURRENT_USER\Software\Microsoft\Windows\Curre ntVersion\Explorer\Advanc
ed]
"Hidden"=dword:00000001
"ShowCompColor"=dword:00000000
"HideFileExt"=dword:00000000
"DontPrettyPath"=dword:00000000
"ShowInfoTip"=dword:00000001
"HideIcons"=dword:00000000
"ShowAttribCol"=dword:00000001
"MapNetDrvBtn"=dword:00000000
"ClassicViewState"=dword:00000000

Any ideas?