This issue was seen also in previous versions:
Dedicated server with installed OS from a template (here: debian jessie). As a parameter for the installation I could enter my own hostname (mysub01.mytop.tl). The server got also its own hostname (theirsub123.ispname.tl) which remains as an alias.
When it comes to the suggestion for the panel-FQDN the default is
panel.mytop.tl but should be panel.mysub01.mytop.tl?
all have their different IPs each. Any further subdomain (e.g. vu2005.mysub01.mytop.tl) is covered through wildcards.
mytop.tl itself is unused. With the current behaviour all machines would get the same panel-FQDN.
Not severe as one can change this value.