From MacOSXHints: “Apple’s Automator Action Installer template (available from Apple’s Installation Instructions for Developers page) is the recommended way to ship custom actions, and it works pretty well. However, one annoyance is its tendency to hide active apps when it runs. Luckily, the fix is easy.”
Contents/Resources/Scripts, and open
main.scptin the Script Editor.
set visible of (every process whose.... In the version of the installer I have, this is line 34.