Actually... never mind.  Panicked prematurely.  We are handling the 
cloned object correctly in IMP; the problem was that, when cloning a 
MIME part, we were doing so even if the part contained no contents 
which was causing IMP to not download the body data.  This should be 
fixed.

Changes have been made in Git (master):

commit 44e27f5cbc9c53651e7b72c8c54ccfd335edd03b
Author: Michael M Slusarz <slusarz@horde.org>
Date:   Tue Nov 18 13:53:18 2014 -0700

     Bug #13700: Don't clone contents if they don't exist

     This makes it look like the contents have always been set in the part,
     even though that may not be true.

  framework/Mime/lib/Horde/Mime/Part.php |    4 +++-
  1 files changed, 3 insertions(+), 1 deletions(-)

http://github.com/horde/horde/commit/44e27f5cbc9c53651e7b72c8c54ccfd335edd03b

Changes have been made in Git (master):

commit af0d2fe1b82799a99ac832a0e1278b7e8dd219b9
Author: Michael M Slusarz <slusarz@horde.org>
Date:   Tue Nov 18 13:47:15 2014 -0700

     Revert "[mms] Don't clone objects when returning data from the 
structure object."

     This reverts commit e3e7fcdacbf34a6863474a5426d0a661e3ee952e.

     This is not correct, since we want the data stored in the cache to be
     pristine.

     See Bug #13700

  .../lib/Horde/Imap/Client/Data/Fetch.php           |    8 ++++----
  framework/Imap_Client/package.xml                  |    2 --
  2 files changed, 4 insertions(+), 6 deletions(-)

http://github.com/horde/horde/commit/af0d2fe1b82799a99ac832a0e1278b7e8dd219b9

This is being worked on.

Unfortunately, this is due to a nasty bug in Horde_Mime_Part where 
cloning is broken.  This was fixed, but the problem is that IMP 
*relied* on that broken behavior (via Horde_Imap_Client).

So I am really uncertain of what to do since correctly fixing 
Horde_Mime breaks installations that upgrade libraries only.  We can 
release a new version of IMP, but EVERY installation before IMP 6.2.4 
will be broken if they upgrade Horde_Mime in the future.  But keeping 
this broken behavior in Horde_Mime is not an option either.

   But fixing cloning there breaks IMP behavior.

If you use a cache in the backend configuration (tried sql and 
hashtable), replying is broken, because the message text from the 
original message gets lost.