New
#571
That's not a bug per se, that's just the new way Explorer Tree View shows various locations. It lists all external devices. If you collapse your This PC, it looks as it should, expandable This PC, under it all external devices all with their individual, expandable entry.
Of course this is stupid and I hope Microsoft will remove those external devices fro the trree view in future builds; they are not needed as they already "belong" to This PC and are viewable there.