this works at my sites. Fine work!

Try this?

Changes have been made in Git (FRAMEWORK_5_2):

commit d2859c9b169074e3ee50abeea59a4baccbcf5c8a
Author: Jan Schneider <jan@horde.org>
Date:   Mon Jan 19 14:46:05 2015 +0100

     Fix setting value of option tag (Bug #13806).

  imp/js/contacts.js |    8 +++++---
  1 files changed, 5 insertions(+), 3 deletions(-)

http://github.com/horde/horde/commit/d2859c9b169074e3ee50abeea59a4baccbcf5c8a

Changes have been made in Git (FRAMEWORK_5_2):

commit 20c254fbb42bf4a62ee41d6a238f88952c36f85b
Author: Jan Schneider <jan@horde.org>
Date:   Mon Jan 19 14:32:46 2015 +0100

     Useful variable names (Bug #13806).

  imp/js/contacts.js |   20 ++++++++++----------
  1 files changed, 10 insertions(+), 10 deletions(-)

http://github.com/horde/horde/commit/20c254fbb42bf4a62ee41d6a238f88952c36f85b

I confirm this bug.
This patch revert the js from 6.2.5 to 6.2.4 and will fix it.

--- imp/js/contacts.js.orig     2015-01-15 02:54:06.000000000 +0900
+++ imp/js/contacts.js  2015-01-19 10:08:56.000000000 +0900
@@ -51,7 +51,7 @@
                      if (!$A(d).any(function(j) {
                          return this.sameOption(f, i, j);
                      }, this)) {
-                        option = this.text.rcpt[f] + ': ' + i.value;
+                        option = f + ': ' + i.value;
                          d[l++] = new Option(option, option);
                      }
                  }

Can confirm this issue here as well, downgrade to IMP 6.2.4 help for 
the moment.

Here is the JS error:

TypeError: element is null prototype.js:6005

You'll need to track down the actual javascript issue then.

I run horde-clear-cache and also used different browser and still 
doesn't work.

Works fine here.  Make sure you have cleared your browser cache.

How to reproduce (dynamic mode):
1.) Start composing new mail.
2.) Click on 'To', so address book will open.
3.) Choose addresses.
4.) Click on 'Ok' and see that none addresses were added.