At present, if you want to create a new theme part (which I try to do for all the little things, so that they’re nicely encapsulated), you have to:
- Click “New theme” and give it a name.
- Load your parent theme.
- Choose the new theme from the list, click “Add”, then save.
It’d be great if, when you create a new theme, you can choose its parent; that way, there’s none of the switching back-and-forth.