The postinstall script does

if ! grep -q "^key" /etc/named.conf; then
  KEY=`cat /etc/rndc.conf |grep secret |head -n1`";"
  if [ -n "$KEY" ]; then
cat >>/etc/named.conf <<EOF
key "key" {
        algorithm hmac-md5;
$KEY
};
EOF
  fi
fi

The problem is

# cat /etc/rndc.conf |grep secret |head -n1
        secret
"c3Ryb25nIGVub3VnaCBmb3IgYSBtYW4gYnV0IG1hZGUgZm9yIGEgd29tYW4K";

It puts `;;' in /etc/named.conf. I got

Mar 11 13:51:53 ocean named[3848]: loading configuration from
'/etc/named.conf'
Mar 11 13:51:53 ocean named[3848]: /etc/named.conf:56: parse error near ;
Mar 11 13:51:53 ocean named[3848]: loading configuration: failure
Mar 11 13:51:53 ocean named[3848]: exiting (due to fatal error)

Removing the extra `;' fixed my problem.