Full user name shown in single chats, only logon name shown in chatrooms?

Hi,

we are using Spark and Openfire since years.

But now i changed the whole logins and insert the name and surname for every user.

In single-chats it is working without any problem, but in the chatrooms only the login name will be shown and not name and surname.

Is there any possibility to change it or is it a bug?

Thanks in advance

Jens