tb 2.8.0 problem with externhost in sip_nat.conf

I do not know if this should be a bug report or not, so I'm simply posting it in the help section.

I was having no end of trouble getting audio to work to a soft phone (X-Lite) when I brought my laptop out of the network to another network. Finally I changed my sip_nat.conf from using externhost to using externip and everything started working.

externhost=pbx.mydomain.com <-- no audio (rarely I would get one way audio)
externip=xxx.xxx.xxx.xxx <-- good audio, no issues

If I log in as root and perform nslookup, I receive the following:

#nslookup pbx.mydomain.com
Server 10.0.0.254
Address 10.0.0.254#53

Non-authoritive answer:
pbx.mydomain.com  canonical name = mysubdomin.dyndns.com.
Name:   mysubdomin.dyndns.com
Address xxx.xxx.xxx.xxx

My sip_nat.conf

nat=yes
;externhost=pbx.mydomain.com
externip=xxx.xxx.xxx.xxx
localnet=10.0.0.0/255.255.255.0
externrefresh=20

This is all the correct information, so I can only assume I have no DNS issues on my trixbox machine. My IP address has not changed in a year, but that's not the point. It could change at anytime if AT&T (my ISP) changes their IP policy.

My trixbox is set to DHCP but the address is reserved in the local router. The DNS is set to the local router by DHCP and all DNS calls seem to be working perfectly.