Looking through the code, this really looks fixed if not in Karmic, then definitely in Lucid and later releases. That's what the "no-auto-default=<mac address>," key in /etc/NetworkManager/nm-system-settings.conf is for, and is automatically added when Auto eth0 is created so that it doesn't get re-added if deleted.
Since we're talking wildly different code between 0.7 and 0.8, please open a new bug using ubuntu-bug (and tell us the number here) if you see that it is still broken in Karmic or Lucid.
Looking through the code, this really looks fixed if not in Karmic, then definitely in Lucid and later releases. That's what the "no-auto- default= <mac address>," key in /etc/NetworkMan ager/nm- system- settings. conf is for, and is automatically added when Auto eth0 is created so that it doesn't get re-added if deleted.
Since we're talking wildly different code between 0.7 and 0.8, please open a new bug using ubuntu-bug (and tell us the number here) if you see that it is still broken in Karmic or Lucid.