Changes have been made in Git (master):

commit a0a96a550aff6839d5e8d78b6e02af7d5a055f7c
Author: Michael M Slusarz <slusarz@horde.org>
Date:   Mon Jun 9 13:13:48 2014 -0600

     Bug #13207: Fix updating signature hash when switching identities

  imp/js/compose-dimp.js |   13 +++++++++----
  1 files changed, 9 insertions(+), 4 deletions(-)

http://github.com/horde/horde/commit/a0a96a550aff6839d5e8d78b6e02af7d5a055f7c

Message 'You have edited your signature. Change the identity and lose 
your changes?' is displayed even if i didn't change the signature, i 
just opened it. Also, when the signature part of compose window is 
opened, try to change identities few times and see that the message 
keeps showing.