Thanks for your patience guys. This has been a nasty bug to track down. In fact, I still haven't figured out the exact cause.

But I have a temporary fix.

Please open /include/staff/header.inc.php and comment out lines 52 - 56 so that it looks like this:

 <!--<?php if($ost && ($headers=$ost->getExtraHeaders())) {
echo "\n\t".implode("\n\t", $headers)."\n";
}
?>-->

I will release osTicket 1.12 (Revision 4) over the weekend which will include this workaround while I continue to look for a proper fix.

Kindly disregard my last message. 

The real fix is to open /include/staff/footer.inc.php and simply change line 16 from

<!-- osta -->

to

</div>

Or upgrade to the latest release, available now.

Thank you both for bringing this issue to my attention!

Excellent! I will download the latest release and let you know!

Thanks!