This is not enough information to even see whether this is expected or really a bug. I suggest you try this first:

$ccbcc = imap_header($mbox,$msgid);
var_dump($ccbcc);

Dear Team,
Consider this example,
I sent email to 3 different email address and cc'ed to another different two email address. When I tried to receive all the email address using imap_header i got the 2 cc'ed email address but not the 3 to address with the same loop and functions.

Please find the output for 
$ccbcc = imap_header($mbox,$msgid);
print_r($ccbcc);

Here Iam getting the expected output for cc but not with the to address whereas the same is fine with Gmail.

stdClass Object
(
    [date] => Sun, 27 Jul 2008 21:04:37 +0530
    [Date] => Sun, 27 Jul 2008 21:04:37 +0530
    [subject] => Testing for multiple email address
    [Subject] => Testing for multiple email address
    [message_id] => <9bfeef6e0807270834t58af4da7v907d2fa51a95c316@mail.gmail.com>
    [toaddress] => info@grafotech.org
    [to] => Array
        (
            [0] => stdClass Object
                (
                    [mailbox] => info
                    [host] => grafotech.org
                )

        )

    [fromaddress] =&gt; Arunkumar Vijayakumar <arun.magzion@gmail.com>

    [from] =&gt; Array
        (
            [0] =&gt; stdClass Object
                (
                    [personal] =&gt; Arunkumar Vijayakumar
                    [mailbox] =&gt; arun.magzion
                    [host] =&gt; gmail.com
                )

        )

    [ccaddress] =&gt; mohan@grafotech.org, arun.magzion@gmail.com
    [cc] =&gt; Array
        (
            [0] =&gt; stdClass Object
                (
                    [mailbox] =&gt; mohan
                    [host] =&gt; grafotech.org
                )

            [1] =&gt; stdClass Object
                (
                    [mailbox] =&gt; arun.magzion
                    [host] =&gt; gmail.com
                )

        )

    [reply_toaddress] =&gt; Arunkumar Vijayakumar <arun.magzion@gmail.com>

    [reply_to] =&gt; Array
        (
            [0] =&gt; stdClass Object
                (
                    [personal] =&gt; Arunkumar Vijayakumar
                    [mailbox] =&gt; arun.magzion
                    [host] =&gt; gmail.com
                )

        )

    [senderaddress] =&gt; Arunkumar Vijayakumar <arun.magzion@gmail.com><title>Grafotech(R) Magzion Mail</title>
    [sender] =&gt; Array
        (
            [0] =&gt; stdClass Object
                (
                    [personal] =&gt; Arunkumar Vijayakumar
                    [mailbox] =&gt; arun.magzion
                    [host] =&gt; gmail.com
                )

        )

    [Recent] =&gt;  
    [Unseen] =&gt;  
    [Flagged] =&gt;  
    [Answered] =&gt;  
    [Deleted] =&gt;  
    [Draft] =&gt;  
    [Msgno] =&gt;   42
    [MailDate] =&gt; 27-Jul-2008 10:34:55 -0500
    [Size] =&gt; 2331
    [udate] =&gt; 1217172895
)

Unfortunately this is how c-client works. PHP merely wraps around the functions provided by that library. 

Dear Team
Your reply is not clear, If it so then thats a bug right ?