Of course, now I am not seeing any of the incorrectly sorted email in 
my inbox. Going to assume it was a transient issue, will open another 
bug if I see it reappear.

Thanks.

It would be the 'datesort' pref.  Although, before you change that, is 
it possible to do a bit of IMAP logging to ensure that the right sort 
algorithm is being used?

The empty mailbox issue appears to have been resolved for me, but (and 
this might be that I am missing the correct config somewhere), I am 
still seeing very strange sorting behavior.  You say that the code now 
no longer sorts by the date in the header, but from the server's 
internal date by default. I am constantly getting new messages 
inserted in the middle of my mailbox listings. How can I change this 
from the default to something that would work as expected for me?

Works for me.

I've pushed some changes to the sort code in IMP - might want to try 
that to see if it helps things.

Also, be aware that date sorting recently changed in IMP.  Date sort 
no longer occurs by the header date, but rather the internal date (at 
least by default).

I'm also seeing some strange sorting, when sorting by Date, I'm 
getting some new email that is being placed somewhere in the middle of 
my list, while others are getting placed correctly.

I didn't really wake up yet. The error *message* is the same, but on a 
different place in the code, actually at the same line like in bug 
#8961:

( ! ) Notice: Undefined index: sort in 
/home/jan/horde-git/framework/Imap_Client/lib/Horde/Imap/Client/Base.php on 
line 1476
Call Stack
#        Time        Memory        Function        Location
1        0,0051        686992        {main}( )        ../mailbox.php:0
2        0,5178        14019660        IMP_Mailbox->buildMailboxPage( NULL, NULL, ??? 
)        ../mailbox.php:227
3        0,5178        14019776        IMP_Mailbox->_buildMailbox( )        ../Mailbox.php:491
4        0,5372        14288380        IMP_Search->imapSearch( 'INBOX.horde.cvs', NULL, 
array ('sort' => array (0 => '0'), 'reverse' => TRUE) 
)        ../Mailbox.php:320
5        0,5372        14288540        Horde_Imap_Client_Base->search( 'INBOX.horde.cvs', 
NULL, array ('sort' => array (0 => '0'), 'reverse' => TRUE) 
)        ../Search.php:344

I spoke too early. I have gone through all kind of folders now, and 
I'm now seeing this error message too, even with a cleanly upgraded 
preference. This happens with mailboxes (originally) sorted by date.

In my case, the prefs got corrupt by using the same prefs table with 
FW_3 and Git. Try running the upgrade task with a fresh prefs table 
copy of a FW_3 install.

Hm... running the upgrade task (again) does not help - but manually 
re-sorting the mailbox by *anything* seems to fix the display.

I guess this bug is "not a bug", but maybe it's an issue with the 
upgrade task?

I thought it was similar, but the errors are in different places.
Some of the affected folders could be, but not all of them.

Duplicate of Ticket #8961 (are these mailboxes sorted by thread?)?

Viewing folders that I know contain messages results in IMP showing 
them empty, with the following log entry:

2010-04-14 18:48:46: (mod_fastcgi.c.2570) FastCGI-stderr: PHP Notice:   
Undefined index: sort in /horde/horde/imp/lib/Mailbox.php on line 321
PHP Stack trace:
PHP   1. {main}() /horde/horde/imp/mailbox.php:0
PHP   2. IMP_Mailbox->buildMailboxPage() /horde/horde/imp/mailbox.php:227
PHP   3. IMP_Mailbox->_buildMailbox() /horde/horde/imp/lib/Mailbox.php:491

It doesn't affect all folders, but I can't pin down the differences 
between the folders that are working, and those that are not.

The value of $res in Mailbox.php is:
array
   'match' =>
     array
       0 => string '31351' (length=5)
       1 => string '31357' (length=5)
       2 => string '31358' (length=5)
...

The working folders contain the sort element, as the code is expecting:

'sort' =>
     array
       0 => string '43858' (length=5)
       1 => string '43857' (length=5)
       2 => string '43856' (length=5)
       3 => string '43855' (length=5)
....