One very specific use case that Installscript MSI allows me to perform is to script one or many other installations along with the main install.
In my case, I sequence one or more different installers during install and one or more during uninstall. This works during install since the setup.exe has an administrator manifest embedded in it. Since all the child installs require admin rights to install this is fine. However on uninstall, a basic MSI project does not save the setup.exe and therefor the admin manifest is not available. During uninstall, the child products do not launch from lack of privilege. The Basic MSI will elevate during the execution sequence. However only 1 install can be active during this time.
The writing of a c++ custom action does present a curious solution.
Would the custom dll be able to elevate even without the admin manifest?
Could you request a rights token from the dll and make it seem like it was coming from the parent installer?
Further, would this prompt only be presented once?
Suppose I had 3 child products to remove. Would the elevation during the execution of the first uninstall be carried over to the second and third using different custom actions? Taken a step further, would any elevation be carried to the parent install so the total number of UAC prompts be 1?
As far as the original problem, I feel more and more that the pop-up is dependent on the environment. On 4 pcs this was executed on, only 2 of them showed this pop-up.