same thing with ftp_quit. Other ftp-functions using the result resource seem to work

Not a bug on the result issue.
void <<< ftp_close.

void returns NULL, which resolves to FALSE.

Could you var_dump($ftp) instead of echoing $result, to see if the resource was freed?

I hope, this is what you were asking for:

<?php 
  $ftp_server = "2.14.128.38"; 

  $ftp = ftp_connect("$ftp_server"); 
  echo("FTP: "); var_dump($ftp); echo("\n"); 

  ftp_close($ftp);
  var_dump($ftp);

?>

results in this:

Unaligned access pid=19673 <php> va=0x140064c8c pc=0x1201ba050 ra=0x1201ba044 inst=0xb4010000
FTP: resource(4) of type (FTP Buffer)

resource(4) of type (Unknown)

marking as feedback until Sebastian responds. 

Sebas,

is the unaligned access issue, part of this problem, or a larger one? Because the ftp_close issue, is expected behaviour:
$ cat test.php
<?php
include('pass.php');
$cs = mysql_connect('localhost:/sql/tmp/mysql.sock', $user, $password);
var_dump($cs);

mysql_close($cs);
var_dump($cs);

$fp = fopen('file.txt', 'w');
var_dump($fp);

fclose($fp);
var_dump($fp);

$ftp = ftp_connect($ftp_server);
var_dump($ftp);

ftp_close($ftp);
var_dump($ftp);

?>
--OUTPUT--
$ !php
php -f test.php 
resource(5) of type (mysql link)
resource(5) of type (Unknown)
resource(6) of type (stream)
resource(6) of type (Unknown)
resource(7) of type (FTP Buffer)
resource(7) of type (Unknown)

Kindof disturbing that the type remains resource, but it has never bothered me IRL :-)

Yes well... But the most important thing is this:

  if (ftp_close($ftp)) { 
    $result = 1; 
  } else { 
    $result = 0; 
  } 

result is 0 in this case as described below which means that ftp_close returns false even on success. So how to check if the connection was closed?

The unaligned access thing happens since... I don't remember when, but see bugs 18588, 18288, 18623, 17449 for some examples.

It's a void function, returning nothing. And nothing == FALSE.
Make the last bit:
if(ftp_close($ftp) === FALSE)
{
        $result=0;
}
else
{
        $result=1;
}
var_dump($ftp);

var_dump($result);

---OUTPUT---
resource(5) of type (mysql link)
resource(5) of type (Unknown)
resource(6) of type (stream)
resource(6) of type (Unknown)
resource(7) of type (FTP Buffer)
resource(7) of type (Unknown)
int(1)

Than change it to:
if(ftp_close($ftp) === NULL)

Whether it should remain a void function is a feature request.

Maybe it should be changed like below, but that's up to Andrew and Stefan.
Index: php_ftp.c
===================================================================
RCS file: /repository/php4/ext/ftp/php_ftp.c,v
retrieving revision 1.65
diff -u -r1.65 php_ftp.c
--- php_ftp.c   26 Jul 2002 22:00:25 -0000      1.65
+++ php_ftp.c   30 Jul 2002 16:41:50 -0000
@@ -1021,7 +1021,10 @@

        ZEND_FETCH_RESOURCE(ftp, ftpbuf_t*, &z_ftp, -1, le_ftpbuf_name, le_ftpbuf);

-       zend_list_delete(Z_LVAL_P(z_ftp));
+       if(zend_list_delete(Z_LVAL_P(z_ftp)) != SUCCESS)
+       {
+               php_error(E_NOTICE, "Could not close ftp stream");
+       }
 }
 /* }}} */

Yes. It would be great to make this a feature like mysql_close that also returns TRUE if it succeded or FALSE if it failed.

This bug has been fixed in CVS. You can grab a snapshot of the
CVS version at http://snaps.php.net/. In case this was a documentation 
problem, the fix will show up soon at http://www.php.net/manual/.
In case this was a PHP.net website problem, the change will show
up on the PHP.net site and on the mirror sites.
Thank you for the report, and for helping us make PHP better.

fixed in HEAD. ftp_quit/close return now TRUE or FALSE.