It's hard to say specifically, but my guess is that subparseform.lib is buggy. (That's a reasonable guess anyway.) You can achieve the same effect with:

#!/usr/local/bin/perl -w

use strict;
use CGI qw(:standard);
print header();

print "Whatever HTML here...\n";

foreach my $key (sort param()) {
    if (param($key)) {
        print "<P><i>Your Teacher input is:</i><B>", param($key), "</B
+>\n";
    }
}
[download]

As web browsers generally miss standards by margins exceeded only by form parsers, it may be a line ending problem, or a character encoding problem. It's better to stick with CGI.pm in this case, as it handles just about anything anyone could ever throw at it.