SmartApp instances at Installed SmartApps screen

When does a SmartApp instance get listed at the Locattion > Installed SmartApps screen ? I am developing a web service SmartApp, and when I try to authorize / install that app from different mobile devices (via my own iOS and Android Apps) and using different combinations of authorized devices, some times a new instance of app is added to the list and sometimes it just replaces the prior instance of the smart app.