AFAIK the problem is that ispcp expects the admin panel to be located under "xxxx.server.domain.tld" (xxxx being admin by default), so it creates a "server.domain.tld" zone file using the "db_master.tpl" part.
You are using "xxxx.domain.tld" instead, so when you install it creates a "domain.tld" zone file using the "db_master.tpl" part.
Then you add "domain.tld" as a hosted domain through the panel, and it creates a "domaint.tld" zone file using "db_e.tpl" parts (which has no "admin" entry)... and overriding the "master" zone file created before!
IMHO this is an ispcp bug and you should create a ticket