Changes have been made in Git (master):

commit a682863da3d43e80ac600abe143e73764a795061
Author: horde@albasoft.com <horde@albasoft.com>
Date:   Tue Dec 4 12:45:25 2012 -0500

     Bug #11806  Must encode headers before sending to the mailer.
     Signed-off-by: Michael J Rubinsky <mrubinsk@horde.org>

  .../Core/lib/Horde/Core/ActiveSync/Driver.php      |    4 ++--
  1 files changed, 2 insertions(+), 2 deletions(-)

http://git.horde.org/horde-git/-/commit/a682863da3d43e80ac600abe143e73764a795061

Nevermind, I was slightly confused :)

Unfortunately your patch isn't acceptable since it would break headers 
containing non-ascii characters that *are* correctly sent from the 
device or are, for whatever reason, not sent as utf-8 encoded.

*sigh* The specs say the device is supposed to send a fully formed 
IMF/RFC5322 email string. I can confirm that, at least on several 
Android devices it is indeed sending UTF-8 characters in the headers.

When I send a message from my device to a recipient containing 
iso-8859-1 chars, I get an email with no encoded message headers.
Sending to "José" <xx@xx.xx> (acute e) delivers a message with a 
header containing utf8 chars like:
   To: José <xx@xx.xx>
but it should be:
   To: =?utf-8?b?Sm9zw6k=?=  <xx@xx.xx>

I think there are some errors in Core/ActiveSync/Driver.php with 
charset handling. At line 1072:
    $h_array = $headers->toArray();
but changing it to
    $h_array = $headers->toArray(array('charset' => 'UTF-8'));
fixes the error and the message headers are correctly coded.
If this is correct, i guess this has to be fixed also in line 1183, in 
copy to sent folder:
$msg = $copy->toString(array('headers' => 
$headers->toString(array('charset' => 'UTF-8'))));