This is the dumbest thing I've ever come across in a WSYIWYG editor in 30 years of making web pages. I get that they want the page to be able to reflow and resize to fit any screen, but this could be fixed easily.
For example, say you're in the middle of a long page and you don't want 30 pages of design ruined when you add a space to a text block. Then, you add a Subsection Block, which would treat everything below as a new section with separate layout, except encapsulated inside the original section. So it wouldn't have it's own section settings, but would use the same settings as the original section.
Alternately, they could have an option to cut a section at any point, splitting it into two sections. It would be a scissors icon you click and it draws a red dotted line on the page that you can move where you want, then click CUT and boom, two sections.
There are lots of ways they could fix it and it's sad they haven't come up with one themselves.