I have a Wix project that I have set to allow major upgrades. I'm using WixUI_Advanced for a choice between per-user and per-machine installs. When I install and upgrade per-user everything works as expected, the installer recognizes an upgrade and there is only one entry in Programs and Features. However when I choose a per-machine install, it starts duplicating entries in Programs and Features (even when both install and upgrade are per-machine and to the same folder).
Looking at the install log file it seems that FindRelatedProducts is executing before the user gets a chance to select a per-machine install, so the installer thinks that the context has changed and won't do an upgrade. I attempted to suppress FindRelatedProducts in InstallUISequence but when I do that the installer still skips FindRelatedProducts in the InstallExecuteSequence.
What are my options at this point?
You could manually execute the FindRelatedProducts action again, after the installation context was selected. Use the MsiDoAction method. I used this approach once and it seemed to work.
A better approach would be to run your own custom action before FindRelatedProducts that would search for a previous version of the product already installed. That custom action should set ALLUSERS to either 1 or to Nothing depending on the scope of that previous version, so that FindRelatedProducts finds it and schedules its upgrade. A good idea would then be to disallow selecting the per-user scope for the user if the previous version was installed per-machine - otherwise the installer may have insufficient privileges to upgrade the previous per-machine installation.
This seems to be the approach taken by InstallShield. If you create an empty test MSI package with the free InstallShield Limited Edition and then de-compile it with Dark, you will see that that custom action is called IsSetAllUsers and located in SetAllUsers.dll.
来源：https://stackoverflow.com/questions/8765214/wix-major-upgrade-and-install-context-issues