Mantra: Getting the header font different from the general font

Hi,
Loving the theme, but having a few issues with the fonts… If I change the general font, then that of the header will change along with it; when I try to change the font under ‘headings font’ nothing happens, and the header stays in the same style as the general writing.

(I hope all that made sense!)

Does anyone know what it is I’m doing wrong? If so, I’d really appreciate your help!

Thanks, Beth