I updated to 2.1.2 and found the default SMF Default Theme - Curve2 comes up twice in the Themes and Layout Settings, see attached caps. I'm wondering if I could remove one of them under Theme Settings? I'm reluctant to do so in case it removes the default theme completely.
You should be able to remove it from the settings, removing a theme does not remove the files associated to it - so the other Curve2 should still work just fine after the other one has been removed. But, as I can't really figure out how that happened to begin with, I'll just remind you that having fresh backups when doing changes is always a good idea.