Silent substitution of unexistent font parts

["Dmitry G. Mastrukov" <dmitry taurussoft org>]

Hi!
I downloaded Bitstream Vera fonts, installed them and tried to use. I
looked on them through gnome font dialog, through gucharmap and was able
to see Cyrillic on ordinary place. But in reality Vera fonts have no
Cyrillic part. So someone (Pango?) silently substitutes unexistent parts
of one font with another similar font.
Is that a feature or a bug? If that is a feature then what are font
selection and viewer dialogs/programs needed for? I'd like to see how
some letters look in exactly that font and not in another. But I see
parts of another font even without notice.

Regards,
Dmitry