Some users appear twice in chat client

Hi community,

i have installed Openfire and it is running quite decently, fulfilling all desired functions. However some users appear twice in our chat client (Spark, Pidgin), with kinda same/different JIDs for example: AND Lastname. So as you can see they appear with only Lastname and Firstname Lastname.

Additional Information:

LDAP authentication is enabled and domain users are using different chat clients.

Does anyone know why it’s like this?