asterisk users - Dec 2004 - My firefly is changing the IP address !!???

I cannot see it!!

I have installed Firefly (third party) and it registers with my server 
with two IP addresses:
Registered '611' (AUTHENTICATED) at 192.168.250.119:4569     (that is my
desktop on the internal LAN)
Registered '611' (AUTHENTICATED) at 192.168.250.254:4569     (that is my
servers internal LAN port)

The registering changes every 10 seconds or so. As long I am on the 
right IP, I can use it, ....

Any hints?

bye

Ronald