Adding a new folder for synchronisation, excluding some sub-folders

I am facing a bit of a problem when I try to add a new folder for synchronisation: I see no possibility to exclude local sub-folders when adding a new folder, even when I pause all synchronisation before. I can choose which remote sub-folders I want synch, but not the local ones.

When I deselect local folders later, I am told that unselected folders will be deleted from my local file system, which is definitely not what I want!

I guess I must be doing something wrong there. So, what is the correct way to add a local folder, but not each of its sub-folders?