Php глюк или как это понимать?

Form prosto dlia otpravki fila, i img.

<form action="save.php" method="post" enctype = "multipart/form-data">
<input type = "text" name = "myname">

<input type = "file" name = "userfile">

<input type = "submit">
</form>

prinimaet drugoi file, ili tot zhe.

echo $myname;
echo $userfile;

esli to zhe samoe zakrit v function,
to $myname vidit, a $userfile net.
esli obiavit' $userfile kak global, to vse
ok.

Vopros, pochemu?