Page Editor - font size for headings incorrect if page font size is set to alternative value

[Jemt]

If font-size for content area (or header or footer) is set to a value and this value is different from 1em, an alternative size for headings will not be displayed as expected in the page editor.

The problem is known to affect designer elements in the page editor (see this code comment), but unfortunately also any text element such as headings.

The work around is to wrap text elements and designer elements in a <div> (see explaination in code comment mentioned above), but obviously that is not a good solution.

Another obvious work around would be to avoid changing the base font-size of the content area, header, and footer.