There All,
for those who are interested in, we found an answer to this issue.
First of all The tile which is shown on the top of the site is taken from the "Account details => Personal information" section, not from the address book entry.
Therefore you should check on admin side 'User Profile' if the 'Title' field are marqued or not (active/required) for admin and customer. Then you can modify the 'title' on user profile 'personal information' and it works !.
This is what we found out.
Hope this will help someone else.
For additional informations:
http://bugtracker.qtmsoft.com/view.php?id=39969