To reproduce:

1. Open the Contacts app
2. Edit Vincent van G.
   Last URL: => http://localhost:8080/magnoliaAuthor/.magnolia/admincentral#app:contacts:detail;/vvangogh:edit
3. Go to App Launcher.
4. Click the Contacts app tile on the App Launcher to return back to the app.
   => New detail subapp is opened.
   Current URL now: http://localhost:8080/magnoliaAuthor/.magnolia/admincentral#app:contacts:detail

This happens when you return to a content app via App Launcher and when the last active subapp was a detail subapp.

This behavior is a regression compared to 5.7.1.

Note also that the new empty subapp is missing Cancel and Save buttons.

See video for better understanding ¯(ツ)/¯