I don't think this is resolved because I am still having the issue.   
Is this the only file that was updated in this fix or were there others?

This was fixed about a week ago.  I just added a bit more error 
checking tonight.

I want to point out my initial recreation steps were inaccurate.  You 
have to click Delete first before the message gets delivered.  Somehow 
when its on the last message, it wants to goto mailbox view and load 
the tooltip preview for the unread messages on the page but it can't 
for the SPAM message because it was filtered (moved) by Ingo.

I'm talking about Ingo filtering (prefs).  Like I mentioned before 
this happens when I'm on the last message in the folder and I click 
Delete and after I click "Delete" a message gets delivered that will 
be filtered by Ingo (specifically for me the message is a SPAM message 
that gets moved to my SPAM folder).  I have previews/tooltips enabled. 
  Here is the relevant code block:



                         if (!$prev_unread || !$ptr->seen) {

                             $ptr->preview = 
$this->_generatePreview($mailbox, $val);

                             $save = true;

                         }



The error message is complaining about $ptr not being an object.

What filters are you talking about?  This situation occurs all the 
time and I've never had an issue (I use procmail filtering).

If a new message comes in when I'm viewing the last e-mail in the 
INBOX, and that new message will be moved to another folder by a 
filter, then I receive the following error message:



Notice: Trying to get property of non-object in 
/home/www/html/mail/imp/lib/IMAP/MailboxCache.php on line 273



Recreation steps:



1) View the last e-mail in your INBOX

2) From another account send yourself a message that will be filtered 
somehow (and moved to another folder)

3) Wait until the message gets delivered, then delete the message you 
are currently viewing



You should receive the error.