[HarfBuzz] Problem with shaping Serif fonts

[Oliver Meier]

Hello

I recently started playing with harfbuzz and encountered a strange problem.
I don't know what I'm doing wrong, but somehow multiple f's shaped for 
serif fonts like DejaVuSerif or FreeSerif get grouped in pairs or so..

         hb_buffer_set_direction( hb_buffer, HB_DIRECTION_LTR );
         hb_buffer_set_script( hb_buffer, HB_SCRIPT_LATIN );
         hb_buffer_set_language( hb_buffer,
hb_language_from_string("en", strlen("en")) );

         hb_buffer_add_utf8( hb_buffer, "ffff", strlen("ffff"), 0, 
strlen("ffff") );
         hb_shape( hb_ft_font, hb_buffer, NULL, 0 );

         hb_glyph_info_t     *glyph_info =
             hb_buffer_get_glyph_infos(hb_buffer, &glyph_count);

At this point glyph_count=2 instead of 4. In the kerning i see that f's 
are indeed "grouped".

Can someone point me in the right direction, or is this a bug?

Thanks!
Oli