Only other thing I've found that sounds plausible (since no router is involved) is maybe ICS... but I dunno.
Is your Azureus client running on a computer behind Windows XP ICS? ICS is a bad excuse for a router in quite a lot of ways but it can be configured to forward services (read: ports) to other machines in the local network.
To do it:
*On the ICS computer, open Control Panel|Network Connections.
*Right click on your Internet Connection (eg, Local Area Connection X - that accommodates your dial-up/broadband modem connection) and click Properties.
*In the "Local Area Connection X Properties" dialog, go to the Advanced tab.
Now click the Settings... button in the Internet Connection Sharing group.
*You get the Advanced Settings dialog and a list of services.
Click the Add... button to display the Service Settings dialog.
*For "Description of service:", type in something to remind you that this is for Azureus' Distributed DB, eg., Azureus DistDB-T.
*In the "Name or IP address ..." field, type in the local network name of the computer that is running Azureus, eg., livingroom.
*In the "External Port ..." and "Internal Port ..." fields type in the port number you have configured your Azureus to use (the port number in Azureus'
Tools|Options|Connection).
*Choose TCP (should be default) and click the Ok button and you are done. You now have the DistDB-T service in your Advanced Settings dialog.
*You need UDP access to the port as well, so you have to repeat the above steps to add a UDP service. Just change the service name (eg., Azureus DistDB-U) and remember to choose UDP instead of TCP this time.
from
http://www.azureuswiki.com/index.php/NAT_problem
You also may want to try another torrent client (like Utorrent) just to see if it's client-related.