@eseo-fcolas Unfortunately this is a known issue but needs major work which we don’t have time for at the moment: https://github.com/FOGProject/fog-client/issues/116
If you are keen to get this to work you are more than welcome to join in and work on this part of FOG/fog-client.
The other thing I might suggest is that most Linux systems can be configured to pull hostname settings via DHCP. You might want to look into this. Or you can use FOG post-deploy scripting to modify hostname config files on the destination system before doing the first reboot.