dthinker.org NS settings

[zma]

I check the NameServer settings of dthinker.org. The settings seems a little big strange:

$ host -t NS dthinker.org
dthinker.org name server master.dthinker.org.

$ host -t A master.dthinker.org
master.dthinker.org has address 115.231.209.242

To resolve master.dthinker.org, need to query dthinkerer.org's NS. The NS is itself. This seems a infinite loop here.

But the dthinker.org seems working just well by the time I check 20150821 10:53.

So, is my understanding wrong, or do I miss some settings here?