Reserved HTML elements seem to receive a different treatment
in the Style Mappings dialog.
I found that if I created a custom paragraph style and mapped
a heading to this style, RH responded by outputting only a
<p> with no class. Additionally it did not split topics on
this heading either.
Bottom Line:
Map headings only to headings AND be sure NOT to check "User
Defined HTML Tag" in the "FrameMaker Styles Conversion Property
Dialog" ... because it will not work. Seems like the headings in
that column should be fixed to greyed-out.