multi-named instance exist?

[dev_null at zoho.com]

Hello,

I found a strange case on bind server.
when one named was running, I started another one or more (the same) named server again, they all got started successsfully.

this is the ps output:

nobody    28312     1  0 10:10 ?        00:00:00 /usr/local/bind/sbin/named -u nobody
nobody    28359     1  0 10:16 ?        00:00:00 /usr/local/bind/sbin/named -u nobody
nobody    28362     1  0 10:16 ?        00:00:00 /usr/local/bind/sbin/named -u nobody

But at this time named server behaves not normal.
for example, I added a NS record and execute rndc reload, the new record could not be queried.

why this happen? 

Thanks.