In thinking about this further, it’s absence from the interface was the result of plugin’s failure to completely upgrade permission settings.
You see, this upgrade introduced new capabilities which accommodates more flexible calendar permissions.
If you install the Capability Manager plugin, you can assign any user with these capabilities:
aec_add_events: allows a user to add, edit and delete their own calendar events
aec_manage_events: allows a user to add, edit and delete all calendar events
aec_manage_calendar: allows a user to modify calendar settings, control which event fields to display and require, modify categories, and view the activity report
As part of the upgrade process the administrator is assigned all these capabilities, but the upgrade process did not reinitialize the settings (and I need to figure out why) – so as an admin you didn’t see the event until you restarted the plugin and re-saved the settings.
In other words. If you run this update on another client site, first try restarting the plugin and re-saving the settings. If you still don’t see the installation event in the interface, then it represents an additional bug.
Whew!
Hope that clears the air,
Eran