[cairo] Mis-rendered Carlito glyphs at certain scales

[Stephan Bergmann]

I discovered that at least on Fedora with 
cairo-1.13.1-0.1.git337ab1f.fc20.x86_64 and 
google-crosextra-carlito-fonts-1.103-0.1.20130920.fc20.noarch,

> cairo_matrix_t bad = { 68, 0, 0, 103, 0, 0 };
> cairo_select_font_face(
>     cr, "Carlito", CAIRO_FONT_SLANT_NORMAL, CAIRO_FONT_WEIGHT_BOLD);
> cairo_set_font_matrix(cr, &good);
> cairo_move_to(cr, 10, 200);
> cairo_show_text(cr, "ABCDEG..");

draws mis-rendered glyphs (see 
<http://people.redhat.com/~sbergman/carlito.png>; reproducer recycling a 
cairo-demo at <http://people.redhat.com/~sbergman/carlito.c>), while a 
slightly different scale of

> cairo_matrix_t good = { 69, 0, 0, 103, 0, 0 };
> cairo_select_font_face(
>     cr, "Carlito", CAIRO_FONT_SLANT_NORMAL, CAIRO_FONT_WEIGHT_BOLD);
> cairo_set_font_matrix(cr, &good);
> cairo_move_to(cr, 10, 400);
> cairo_show_text(cr, "ABCDEG..");

draws good ones.

What is the most likely component to report this to, the Carlito font, 
Cairo, or somewhere below it on the software stack?

Stephan