I know what this is now: Google Maps loves to leave dropped and obsolete layers on the map: You can cleanse those layers by hovering the mouse over the 'Map' / 'Satellite' square and remove those layers from the drop-down menu.
But this is still just a workaround IMHO - GM needs to be:
1) Smarter - and
2) More informative - WHAT do I see in the map, and WHY?
This reported via the Chrome "Report an issue..." tool.