My output doesn't match yours, even when I do have the terminal in UTF-8. But that doesn't bug me since, as ikegami points out, the string lengths I get are wrong when I use non-ASCII characters:

$ perl -l
use warnings;
use strict;
print length 'ñ';
__END__
2
[download]

Now I wonder how is it possible that I've never encountered any problems with this :^). Thanks!