OK, I've got a fairly minimal failing case: 
#!/usr/bin/perl -wT

use strict;

use CGI qw(:standard);
use CGI::Carp qw (fatalsToBrowser);
#use HTML::Template;

my $initial_page = <<'EOHTML';
<html><head></head><body>

<table width=100% border=0>
<tr><th>Orders</th>
    <td colspan=4>
        Some order<br>
        
</td></tr>
<tr><form name=myform action=test.cgi method=get>
    <td></td>
    <td colspan=3>

      <input type=hidden name=action value=issueorder>
      <input type=hidden name=id id=unitid value=12345>
      <select name=ordertype id=ordertype size=1 style="width:100%"
          OnMouseUp="order_params(['ordertype', 'unitid'], ['orderpara
+ms']);">
        <option value=halt>
             Halt
        <option value=wait>
             Wait
        
      </select>
      <div id=orderparams></div>
    </td>

    <td style="vertical-align:bottom"><input type=submit value='Issue 
+Order'>
    </td>
  </form></tr>
</table>

</body>
EOHTML

require CGI::Ajax;
my $cgi = new CGI();
my $pjx = new CGI::Ajax(order_params  => \&order_params);
print $pjx->build_html($cgi, $initial_page);

exit 0;

sub order_params {
  my $retval = <<'EOHTML2';
<table width=100% border=0>
<tr>
  <th width=10%>Duration</th>
  <td><input type=text name=duration style="width:100%"></td>
</tr>
</table>
EOHTML2

  return $retval;
}

[download]
Using your HTML snippet in $initial_page worked properly, even with your OnChange handler changed to the CGI::Ajax call, so I added HTML::Template back in, stripped down the actual template and tried again. That lost the duration parameter just like the real version does, but using the HTML::Template-generated page body seems to behave identically, so I've put that in and removed HTML::Template. (I did save the stripped-down template and the data I fed it, just in case, but it seems unlikely to be relevant.)

In reply to Re^2: Submitting forms with CGI::Ajax-created fields by dsheroh
in thread Submitting forms with CGI::Ajax-created fields by dsheroh

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