php htmlspecialchars() from one form to another

<?php $_POST['txt'] = htmlspecialchars($_POST['txt']); ?>
<form method="post">
<input name="txt" value="<?=$_POST['txt'] ?>" />
<input type="submit" name="save" value="test" />
</form>

1) Type & into the text field
2) Hit the test button once
3) When the page completes post back, hit the test button again
4) When the page completes post back, view the page source code

<input value="&" />

<input value="&quot" />

$_POST['txt'] == '&';
htmlspecialchars('&') == '&'

txt=&

txt=&&user=soulmerge&pass=whatever