I'm thinking bug. This little program works under ActivePerl 5.8.1.

#!perl
use strict;
use warnings;

$_ = "a\x{2322}bcd\n";
print substr($_, 0, 3), "\n";
[download]

output is:

Wide character in print at try2.pl.txt line 6.
aΓîób
[download]

Or at least that's as close as PerlMonks can display. The important thing is that it prints from a to b.