I use PHP enabled 'track_vars' option in php3.ini.
But arguments don't be appended to $HTTP_POST_VARS array
if enctype is 'multipart/form-data'.

<form method=post action=foo.php3>
<input type=hidden name=hello value=world>
<input type=submit>
</form>

in foo.php3:
echo "hello ",$HTTP_POST_VARS['hello'],"!\n";
echo "goodbye ",$hello,"!\n";

result:
hello world!
goodbye world!

it seems ok, but when:
<form method=post action=foo.php3 enctype="multipart/form-data">
....
</form>

result:
hello !
goodbye world!