Changes have been made in Git (master):

commit 03a643c704071735f6e3ff54636b41a2d08ca779
Author: Michael M Slusarz <slusarz@horde.org>
Date:   Sat May 11 13:52:28 2013 -0600

     Bug #12245: Lost passing options to _fetch()

  .../Imap_Client/lib/Horde/Imap/Client/Base.php     |    4 ++--
  1 files changed, 2 insertions(+), 2 deletions(-)

http://git.horde.org/horde-git/-/commit/03a643c704071735f6e3ff54636b41a2d08ca779

In case it's not obvious, this is a typo:
// Shows HIGHESTMODSEQ is currently 66128

and should read 661128:

array(1) {
   'highestmodseq' =>
   string(6) "661128"
}

I've just noticed that ActiveSync is detecting tons of unnecessary 
changes for email. This is resulting in what looks like a change being 
sent to the client for each email currently in the mailbox, everytime 
a sync is requested. This started sometime in the last few days.  The 
following code demonstrates this:

$imap = $registry->mail->imapOb();
$mbox = new Horde_Imap_Client_Mailbox('INBOX');
$status = $imap->status($mbox, Horde_Imap_Client::STATUS_HIGHESTMODSEQ);

// Shows HIGHESTMODSEQ is currently 66128
var_dump($status);

$query = new Horde_Imap_Client_Fetch_Query();
$query->modseq();
$query->flags();
$fetch_ret = $imap->fetch($mbox, $query, array(
     'changedsince' => '661128'
));

// Returns an array of 43 ids - the total number of emails in the mailbox.
var_dump($fetch_ret->ids());



The resulting imap.log:

------------------------------
S: * OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID 
ENABLE IDLE STARTTLS LOGINDISABLED] Dovecot ready.
C: 1 STARTTLS
S: 1 OK Begin TLS negotiation now.
C: [LOGIN Command - username: mike]
S: 2 OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID 
ENABLE IDLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS 
MULTIAPPEND UNSELECT CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED 
I18NLEVEL=1 CONDSTORE QRESYNC ESEARCH ESORT SEARCHRES WITHIN 
CONTEXT=SEARCH LIST-STATUS] Logged in
C: 3 ENABLE QRESYNC
C: 4 STATUS "INBOX" (HIGHESTMODSEQ)
S: * ENABLED QRESYNC
S: 3 OK Enabled.
S: * STATUS "INBOX" (HIGHESTMODSEQ 661128)
S: 4 OK Status completed.
C: 5 EXAMINE "INBOX" (QRESYNC (1292457115 661128 
119945:119946,130457,158453,158777,159889,160243,163615,166864,167721,167753,168263:168264,169551,169571,169798,173015,173648,174802,175426,178421,178501,178573,179008,179044,179050,179067,179084,179120,179134,179196,179225,179229,179241,179314,179317,179446,179461,179471,179477,179481,179504:179505))
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft $NotJunk 
$forwarded $Junk)
S: * OK [PERMANENTFLAGS ()] Read-only mailbox.
S: * 43 EXISTS
S: * 0 RECENT
S: * OK [UNSEEN 43] First unseen.
S: * OK [UIDVALIDITY 1292457115] UIDs valid
S: * OK [UIDNEXT 179506] Predicted next UID
S: * OK [HIGHESTMODSEQ 661128] Highest
S: 5 OK [READ-ONLY] Select completed.
C: 6 UID FETCH 
119945:119946,130457,158453,158777,159889,160243,163615,166864,167721,167753,168263:168264,169551,169571,169798,173015,173648,174802,175426,178421,178501,178573,179008,179044,179050,179067,179084,179120,179134,179196,179225,179229,179241,179314,179317,179446,179461,179471,179477,179481,179504:179505 
(MODSEQ)
S: * 1 FETCH (UID 119945 MODSEQ (519624))
S: * 2 FETCH (UID 119946 MODSEQ (593415))
S: * 3 FETCH (UID 130457 MODSEQ (550859))
S: * 4 FETCH (UID 158453 MODSEQ (615648))
S: * 5 FETCH (UID 158777 MODSEQ (616275))
S: * 6 FETCH (UID 159889 MODSEQ (618907))
S: * 7 FETCH (UID 160243 MODSEQ (619329))
S: * 8 FETCH (UID 163615 MODSEQ (626599))
S: * 9 FETCH (UID 166864 MODSEQ (634301))
S: * 10 FETCH (UID 167721 MODSEQ (636238))
S: * 11 FETCH (UID 167753 MODSEQ (651301))
S: * 12 FETCH (UID 168263 MODSEQ (637556))
S: * 13 FETCH (UID 168264 MODSEQ (637557))
S: * 14 FETCH (UID 169551 MODSEQ (641138))
S: * 15 FETCH (UID 169571 MODSEQ (651302))
S: * 16 FETCH (UID 169798 MODSEQ (641163))
S: * 17 FETCH (UID 173015 MODSEQ (648169))
S: * 18 FETCH (UID 173648 MODSEQ (651479))
S: * 19 FETCH (UID 174802 MODSEQ (651527))
S: * 20 FETCH (UID 175426 MODSEQ (654759))
S: * 21 FETCH (UID 178421 MODSEQ (658854))
S: * 22 FETCH (UID 178501 MODSEQ (659094))
S: * 23 FETCH (UID 178573 MODSEQ (659294))
S: * 24 FETCH (UID 179008 MODSEQ (659982))
S: * 25 FETCH (UID 179044 MODSEQ (660089))
S: * 26 FETCH (UID 179050 MODSEQ (660110))
S: * 27 FETCH (UID 179067 MODSEQ (660153))
S: * 28 FETCH (UID 179084 MODSEQ (660197))
S: * 29 FETCH (UID 179120 MODSEQ (660451))
S: * 30 FETCH (UID 179134 MODSEQ (661013))
S: * 31 FETCH (UID 179196 MODSEQ (661016))
S: * 32 FETCH (UID 179225 MODSEQ (660599))
S: * 33 FETCH (UID 179229 MODSEQ (660604))
S: * 34 FETCH (UID 179241 MODSEQ (660633))
S: * 35 FETCH (UID 179314 MODSEQ (660770))
S: * 36 FETCH (UID 179317 MODSEQ (660778))
S: * 37 FETCH (UID 179446 MODSEQ (660982))
S: * 38 FETCH (UID 179461 MODSEQ (661011))
S: * 39 FETCH (UID 179471 MODSEQ (661017))
S: * 40 FETCH (UID 179477 MODSEQ (661041))
S: * 41 FETCH (UID 179481 MODSEQ (661042))
S: * 42 FETCH (UID 179504 MODSEQ (661122))
S: * 43 FETCH (UID 179505 MODSEQ (661128))
S: 6 OK Fetch completed.
C: 7 LOGOUT
S: * BYE Logging out