Any news on this subject? I think I experience the same problem when using outside-head for the auto-number-position in a h1 heading class. If I use the definition as copied below for the default medium in the .css, the xml editor shows it correctly but when I make the HTML5 preview or build the output, it shows the chapter title in the font size 12 that I defined for the body.
If I remove mc-auto-number-position: outside-head the preview and the output will show both the same: font size 30 pts. But of course then I loose the advantage of defining the chapter number outside of head.
I found a workaround but not sure to understand the logic behind the workaround: if I add in the css for the media non-print a font size of 30 pts, it will apply it correctly. Very strange! I thought that if h1.ChapterTitle would not be present in the non-print media for the HTML5 output, it would look in the default definition of css.....
h1.ChapterTitle
{
text-align: left;
margin-left: 5.1cm;
margin-right: 0cm;
margin-top: 0pt;
margin-bottom: 180pt;
font-weight: normal;
font-style: italic;
mc-hyphenate: never;
mc-auto-number-position: outside-head;
line-height: 45pt;
text-decoration: none;
mc-auto-number-format: 'GH:CHAPTER {n+}.';
mc-auto-number-offset: 250px;
font-size: 30pt;
}