Squirrelmail, encode changes when replying emails

• SM version 1.4.22 Centos 6.7 PHP 5.3.3 Apache 2.2.15 Plugins:
  1. filters
  2. delete_move_next
  3. message_details
  4. newmail
  5. translate
  6. squirrelspell
  7. set_user_data

last versions Postfix 2.6.6, Dovecot 2.0.9 installed from Webmin CP Tests from Firefox (Ubuntu, XP), Thundirbird (Ubuntu client), Safari Mac

This is a problem about special chars like accented vowels (Spanish language option selected). No problem creating email. Recipient receives it correctly (same in Squirrelmail and Thundirbird).

The problem comes when the recipient answers the sender keeping the original text with those accented vowels or sends a new mail with new ones. Sender receives correctly the replied (or new) message but when he replies again to the recipient those accented vowels are not interpreted correctly.

Below some screenshots.

Sender’s Inbox getting a new email with accented vowels:

Reading incoming email content:

Replying email:

I've contacted SM-i18n group but I didn't get an answer