Font rendering question - Apple Color Emoji.ttc

[Andrew Murray]

Hi,

Over at Python Pillow, a user has tried to render an emoji with macOS’ Apple 
Color Emoji.ttc - 
https://github.com/python-pillow/Pillow/issues/7854#issuecomment-2128088090. 
The emoji is the combination of ‘woman’ U+1F469, 'zero width joiner’ U+200D, 
'manual wheelchair’ U+1F9BD, 'zero width joiner’ U+200D, 'black rightwards 
arrow’ U+27A1, 'variation selector-16’ U+FE0F, with the intention of being a 
woman in a manual wheelchair facing right.

However, FreeType returns an Unimplemented_Feature error. Interesting, it only 
doesn’t do this for just a woman in a manual wheelchair. To demonstrate, the 
following code attempts to use woman in a manual wheelchair, and then woman in 
a manual wheelchair facing right. The error only occurs in the second instance.

FT_Library library;
FT_Init_FreeType(&library);
FT_Face face = NULL;
FT_New_Face(library, "/System/Library/Fonts/Apple Color Emoji.ttc", 0, &face);
FT_Set_Pixel_Sizes(face, 0, 64);
int error = FT_Load_Glyph(face, 1507, FT_LOAD_DEFAULT);
if (error) {
        printf("1507: error %d\n", error);
}
error = FT_Load_Glyph(face, 1508, FT_LOAD_DEFAULT);
if (error) {
        printf("1508: error %d\n", error);
}

I’ve attached images that, as far as I can see, show that both indexes are 
present in the font.

Any thoughts as to why one should fail but not the other would be appreciated. 
Thanks.