I just had a strange thing occur. I was fighting with a Messages server problem as described here : https://discussions.apple.com/thread/4322859?start=0&tstart=0 and was alternating back and forth between an upgraded boot drive, where Messages was not working, and a fully functioning backup boot drive. Two physically separate disks on the same system.
A solution to the problem above was to manually delete Server.app from the boot drive, reboot, and reinstall Server.app from App Store.
Working on the non working (Messages Server) upgraded drive which was the boot disk, I removed Server.app and rebooted. There is now no Server.app on this drive.
Log in to App Store and ask for install of Server software. Did not receive a drive selection request. Assumed install would be on boot disk.
App Store had upgraded my backup drive to the new Server.app. The boot drive still did not have Server.app on it.