http://bugs.freedesktop.org/show_bug.cgi?id=21197
--- Comment #1 from Werner Lemberg wl@gnu.org 2009-04-15 09:02:01 PST --- Reading the redhat bug description I see that you are not using the TT hinter.
With the autohinter I fear this problem is unavoidable. It probably has to be handled on a level higher than FreeType: If you pass a font to the library, the autohinter simply doesn't know that the digits 0-9 are intended to have the same width. As you certainly aware there are fonts containing `old digits' which intentionally have different widths.
I can imagine that there is an option to `fontconfig' which forces the same width to all digits if the autohinter is used (probably using the average value of all digit widths).