Why is slave zone different from master zone..?

[Ronni Jensen]

Hi,

On my master NS I have this reverse map:

-----------
$TTL 86400      ; 1 day
$ORIGIN 64.65.66.IN-ADDR.ARPA.
@                       IN SOA  ns1.xxx.dk. dns.xxx.dk. (
                                2006071305 ; serial
                                10800      ; refresh (3 hours)
                                3600       ; retry (1 hour)
                                1209600    ; expire (2 weeks)
                                86400      ; minimum (1 day)
                                )
                        NS      ns1.xxx.dk.
                        NS      ns2.xxx.dk.

; Begin
2                       PTR     ns1.xxx.dk.
; End
-----------

But when this zone has been AXFR'ed to my slave NS, it comes to look
like this:

-----------
$ORIGIN .
$TTL 86400      ; 1 day
64.65.66.in-addr.arpa   IN SOA  ns1.xxx.dk. dns.xxx.dk. (
                                2006071305 ; serial
                                10800      ; refresh (3 hours)
                                3600       ; retry (1 hour)
                                1209600    ; expire (2 weeks)
                                86400      ; minimum (1 day)
                                )
                        NS      ns1.xxx.dk.
                        NS      ns2.xxx.dk.
$ORIGIN 64.65.66.in-addr.arpa.
2                       PTR     ns1.xxx.dk.
-----------

Can someone explain to me, why the $ORIGIN directive is being moved from
the top of the zone to the resource record(s) area - and the @ wildcard
in the SOA record is replaced with $ORIGIN value?

Should I construct my master zone differently, or is the design ok?

Thank you
/Ronni