Changes have been made in Git (master):

commit 317d201eadff7d98083e3bbb1f6d2bafd5da669b
Author: Moritz Venn <ritzmo@php.net>
Date:   Wed Jul 11 11:27:54 2007 +0000

     Fix #11578 by adding <code><pre> to Syntax of Code and switching 
Parsing order with Preformatted


     git-svn-id: 
https://svn.php.net/repository/pear/packages/Text_Wiki/trunk@239478 
c90b9560-bf6c-de11-be94-00142212c4b1

  Text/Wiki/Mediawiki.php            |  2 +-
  Text/Wiki/Parse/Mediawiki/Code.php | 14 ++++++++++----
  2 files changed, 11 insertions(+), 5 deletions(-)

http://github.com/horde/horde/commit/317d201eadff7d98083e3bbb1f6d2bafd5da669b

Haven't seen this in a while.

Ping?  If this is happening, and is reproducible, it should be 
blocking on Horde 5.

The only thing I *think* this could be is the new CONDSTORE sync code 
that searches for deleted messages to remove from the cache.   
Specifically, this search query:

             $squery = new Horde_Imap_Client_Search_Query();
             $squery->ids($this->getIdsOb($uids_ob->range_string));

But $uids_ob is created from $uids, and this is not done unless $uids 
is non-empty.  $uids is grabbed from the cache.   
$uids_ob->range_string would return an empty string if $uids is a 
non-string, but that is impossible since the cache->get() call can 
ONLY return an array.

The only other thing I can think of is that your Horde_Imap_Client_Ids 
has not been updated in PHP/cache/autoload/etc., so range_string 
doesn't exist and is therefore returning an empty string.

In very rare, unreproducible cases, the following happens recently 
when opening a mailbox for the first time:

S: * OK [CAPABILITY IMAP4rev1 LITERAL+ ID ENABLE  XIMAPPROXY] neo 
Cyrus IMAP v2.
4.16-Debian-2.4.16-1 server ready
C: [LOGIN Command - username: jan]
S: * OK [XPROXYREUSE] IMAP connection reused by imapproxy
S: 1 OK User logged in
C: 2 SELECT "INBOX.horde.bugs" (CONDSTORE)
S: * 108 EXISTS
S: * 0 RECENT
S: * FLAGS (\Answered \Flagged \Draft \Deleted \Seen NonJunk $NotJunk 
$Junk H3 I
ntra2net)
S: * OK [PERMANENTFLAGS (\Answered \Flagged \Draft \Deleted \Seen 
NonJunk $NotJu
nk $Junk H3 Intra2net \*)] Ok
S: * OK [UIDVALIDITY 1082203163] Ok
S: * OK [UIDNEXT 58010] Ok
S: * OK [HIGHESTMODSEQ 8196] Ok
S: * OK [URLMECH INTERNAL] Ok
S: 2 OK [READ-WRITE] Completed
C: 3 UID SEARCH RETURN (ALL COUNT) UID ""
S: 3 BAD Invalid Search criteria
C: 4 STATUS "INBOX" (RECENT)
S: * STATUS INBOX (RECENT 0)
S: 4 OK Completed
C: 5 STATUS "INBOX.horde.apps" (RECENT)
S: * STATUS INBOX.horde.apps (RECENT 0)
S: 5 OK Completed
C: 6 STATUS "INBOX.horde.cvs" (RECENT)
S: * STATUS INBOX.horde.cvs (RECENT 0)
S: 6 OK Completed
C: 7 STATUS "INBOX.horde.dev" (RECENT)
S: * STATUS INBOX.horde.dev (RECENT 0)
S: 7 OK Completed
C: 8 STATUS "INBOX.horde.imp" (RECENT)
S: * STATUS INBOX.horde.imp (RECENT 0)
S: 8 OK Completed
C: 9 STATUS "INBOX.Privat" (RECENT)
S: * STATUS INBOX.Privat (RECENT 0)
S: 9 OK Completed
C: 10 LOGOUT
S: * BYE LOGOUT received
S: 10 OK Completed

Only reloading the whole page gets the mailbox back.