In reply to daniel.

I know there is a ticket for handling specific HTML tags with the Group block. I am unsure if this has been implemented yet. It is a good thing to start identifying these types of issues now rather than later. Any developer tinkering with these themes should go in with the mindset that everything is still in flux and that there are tons of problems we need to overcome. Having block-based themes in the directory makes it easier for more people to test rather than relegating them to a GitHub repo. I don't see this as a bad precedent because they are not meant to be perfectly-constructed themes at this point. They are more of a starting point in which we can identify problems, such as the one you brought up.