[wix-users] Serious problem with FindRelatedProducts and install context

[Alan Sinclair]

I'm making a dual-scope MSI which uses the InstallScope dialog for the user
to choose per-user or per-machine. It installs fine, but upgrades to a
per-machine installation fail.

FindRelatedProducts seems to search only the scope in current force when it
runs, and it's sequenced right at the start (so early it doesn't even
appear in the log.)

My MSI has ALLUSERS=2 and MSIINSTALLPERUSER=1, with the InstallScope dialog
changing that as required, so FindRelatedProducts looks only in per-user
scope.  If an earlier-versioned MSI was installed per-machine,
FindRelatedProducts
does NOT find it, so the install does not upgrade, and Control Panel's ARP
shows the product twice (there's only one set of files, of course).

Is there any way to solve this?  Can FindRelatedProducts be run later in
the sequence, after the UI? Or can FindRelatedProducts be run twice?

Or can I add custom actions before FindRelatedProducts to look in the
registry and check previous install scope, then adjust ALLUSERS etc
accordingly so FindRelatedProducts searches the right scope?

How can a dual-scope package be upgraded in both per-user AND per-machine
installations?

Thanks
Alan