[horde] Weird log error

[Alan Snyder]

I'm getting the following error messages in chunks of about 20 at a
time in some areas and 3 or 4 at a time in other areas of my apache
error_log file. I can't seem to correlate these messages to specific
user actions, but based on the URL, it looks like something to do with
the newmail popup.

[client xxx.xxx.xxx.xxx] PHP Notice:  Trying to get property of
non-object in /var/www/htdocs/horde/lib/Horde/MIME.php on line 664,
referer: https://secure.domain.com/imp/mailbox.php?Horde=clai8olv7rfrinqm4cu7o34l07&no_newmail_popup=1&mailbox=INBOX

Any ideas? Thanks in advance