Note the advertised "Hostname Capability:" neighbor capability:
email@example.com:~$ show ip bgp neighbors 192.168.64.12 BGP neighbor is 192.168.64.12, remote AS 4200000001, local AS 65001, external link Hostname: sandbox.antelope.net BGP version 4, remote router ID 192.168.64.12, local router ID 192.168.79.1 BGP state = Established, up for 00:48:38 Last read 00:00:10, Last write 00:00:18 Hold time is 60, keepalive interval is 20 seconds Neighbor capabilities: 4 Byte AS: advertised and received AddPath: IPv4 Unicast: RX advertised IPv4 Unicast Route refresh: advertised Address Family IPv4 Unicast: advertised and received Hostname Capability: advertised (name: fw1.den1,domain name: n/a) received (name: sandbox,domain name: antelope.net) Graceful Restart Capabilty: advertised ...
The domain name is "n/a" meaning a zero byte domain is set. However, the domain name is set in the configuration:
firstname.lastname@example.org# show system domain-name domain-name antelope.net
I've filed another bug on the FQDN capability, which deals with the hostname portion after an image install + reboot, and appears unrelated to this problem.