Phones won't connect without NAT after Asterisk upgrade?

After upgrading my Asterisk box to 1.4 I found that a few of my phones, a Cisco 7960, Cisco 7940 and S450IP will not connect to Asterisk without using NAT. They are on the same network which consists only of the Asterisk server, a Cisco switch with default settings and the phones. If I enable NAT in the 7960 or 7940 they will connect fine, however the S450IP doesn’t have this option. The only thing that I changed was the Asterisk upgrade, the IP’s and everything are the same. Is there something that I am missing here? Why would I need NAT enabled on the phones operating only in a private network? The phones will connect to the tftp server on Asterisk, but there is nothing in the log files regarding the phone trying to connect via SIP.