Problem with dynamic IP

[Geoff Down]

Hi,
  the Tor FAQs mentions bugginess with how Tor detects the IP of a relay 
when it isn't fixed.
I think I have this problem - the logs show Tor changing the IP it 
advertises to the world for the ORPort even though my IP has not in 
fact changed:

Nov 04 03:47:29.242 [Notice] Our IP Address has changed from xxx to 
yyy; rebuilding descriptor.
Nov 04 03:56:44.210 [Notice] Self-testing indicates your ORPort is 
reachable from the outside. Excellent. Publishing server descriptor.
Nov 04 04:17:58.142 [Notice] Our IP Address has changed from yyy to 
xxx; rebuilding descriptor.
Nov 04 04:19:05.460 [Notice] Self-testing indicates your ORPort is 
reachable from the outside. Excellent. Publishing server descriptor.
Nov 04 04:19:37.005 [Notice] Performing bandwidth self-test...done.
Nov 04 04:38:19.808 [Notice] Our IP Address has changed from xxx to 
yyy; rebuilding descriptor.
Nov 04 04:43:44.802 [Notice] Self-testing indicates your ORPort is 
reachable from the outside. Excellent. Publishing server descriptor.

Here yyy is the false IP - odd that it is supposedly reachable from the 
outside world.
The false IP is however on the right network, and could be one I had 
earlier in the day/week/month. Any idea how to stop this happening 
please? It's Tor 0.2.0.31 (r16744) MacOSX 10.3.9.
  Also, I'm advised to back up my relay's private key 'stored in 
"keys/secret_id_key" in your DataDirectory' . Where is that? I don't 
have a DataDirectory defined in the torrc.

Thanks,
downie