When the load factory-default command is issued to set or delete the system hostname, the hostname is not cleared even though it appears to have cleared from the configuration lines.

This article indicates this is a Junos mgd limitation and clarifies that there is no service impact due to this limitation. Users can reboot the device to clear the system hostname if required.

When you issue load factory-default to set or delete the system host-name, the host-name is not cleared even though it is cleared from the configuration lines.

The following is the testing result for your reference:

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{master:0}[edit]
root@EX4200-3# show system host-name
host-name EX4200-3;

{master:0}[edit]
root@EX4200-3# delete system host-name

{master:0}[edit]
root@EX4200-3# commit
configuration check succeeds
commit complete

{master:0}[edit]
root@EX4200-3# exit
Exiting configuration mode

{master:0}
root@EX4200-3> exit 

root@:RE:0% cli
{master:0}
root@EX4200-3> configure 

{master:0}[edit]
root@EX4200-3# show system host-name

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This is due to a Junos mgd limitation, which is present in all Junos products except the EVO type version.

Since the issue does not have any service impact and customers would set hostname usually, this problem can be ignored.

However, rebooting the device will clear the system hostname if required.