PHP imap_expunge imap_close problem

Hello,

I've searched the docs and online and can't find the solution to my
problem. I'm running PHP 4.0.6 on Mandrake Linux with Sendmail and I've
deployed a PHP based webmail. Problem is that when I use the delete script
it deletes two messages from the inbox (the message passed by url variable
$num and the next message higher in number). The script I have now is
posted below. Problem is that if I comment out the imap_close($mbox) the
script works properly (only one message deleted). Any idea why? Is there a
problem with not invoking imap_close()? Thanks for any help:

$server = "127.0.0.1";

$mbox = @imap_open("{".$server.":110/pop3}INBOX", $username, $password);

imap_delete($mbox, $num);
imap_expunge($mbox);

imap_close($mbox);