We've got a couple of pings on a billboard bug that I thought I'd share in case others are seeing this problem.
In Windows Installer 2 billboards showed one after another smoothly during InstallFiles action. With Windows Installer version 3, billboards showed twice during the install. The first time, the billboards showed during generating script and the second time was as they were displayed normally as in Windows Installer 2.
In MSI 2.0 it was only the GenerateScript action that was sending an ActionStart message while the script was being generated, but now we’re sending the ActionStart message for each individual action that is authored in the .MSI package’s InstallExecute table, while we’re generating the execution script for it. This causes the UI handler to see new actions coming in, to start counting the billboards and - if there are any - to display them in response to progress messages sent by the service.