@operagotcrazy You move all tabs out of their islands so you no longer have any islands and you still see that extra + button?
If so, goto the URL opera://about, take note of the "profile" path, close Opera and delete the "Sessions" folder in the profile folder. That should wipe out all tabs and clear your recently-closed tabs list. Then, you shouldn't see that extra + button anymore unless you create a tab island.
