Well, I finally found some related -rather old- issues in Bugzilla (glib)
http://sources.redhat.com/bugzilla/show_bug.cgi?id=6530
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=208308
http://sources.redhat.com/bugzilla/show_bug.cgi?id=649
The last explains why they do not consider it a bug:
ISO C99 requires for %.*s to only write complete characters that fit below
the
precision number of bytes. If you are using say UTF-8 locale, but ISO-8859-1
characters as shown in the input file you provided, some of the strings are
not valid UTF-8 strings, therefore sprintf fails with -1 because of the
encoding error. That's not a bug in glibc.
It's clear, though it's also rather ugly, from a specification point of
view (we must
count raw bytes for the width field, but also must decode the utf8 chars
for finding
character boundaries). I guess we must live with that.
Hernán J. González
