Go the "Standard Article" page (/demo-project/about/subsection-articles/article) and edit it. You can scroll up and down and you can select the page edit bar and the first area edit bar ("Page header").

If you scroll down, though, and click on the "Content" area bar, the page jumps to the top. The page edit bar and the "Page Header" area edit bar are shown in gray, which suggests that your area bar actually got selected. The Action bar also seems to adjust and offer you to add a new component. However, scrolling no longer works. See attached screen shot for how this looks.

You can fix that by either executing an action or selecting one of the visible bars. Scrolling then recovers again.