Importing Fortigate to Fortimanager, impossible to change name ?

Hi,

Im importing a Fortigate (with some VDOMS) to Fortimanager. All is good and fine - but the issue is that I am unable to change the hostname on the Fortigate after import...or..I can change it, and the fortigate itself gets the new hostname. But even when I refresh my device, push rules..refresh again - The fortimanager keeps showing the old hostname in the device manager. 

Is this just a bug ? Do I have to set the name before i import or is there a workaround for changing this hostname ?