Avahi failing to function, no results returned from avahi-browse

I have two machines running Ubuntu 9.10. On my home server, avahi works correctly, and I get 39 mDNS entries, both IPv4 and IPv6:

# avahi-browse -at | wc
     39 316 3347
#

The list includes my printer, a couple of Macs, AppleTV, and the server itself.

On my laptop, I get diddly squat:

# avahi-browse -atv
Server version: avahi 0.6.25; Host name: T61.local
E Ifce Prot Name Type Domain
: Cache exhausted
: All for now
#

As far as I can tell, both systems have an identical setup--nsswitch.conf the same, /etc/avahi/* the same, so I'm mystified as to what is going on. Nothing seems to show up in /var/log/messages.

$ lsb_release -rd
Description: Ubuntu 9.10
Release: 9.10

$ apt-cache policy avahi-daemon
avahi-daemon:
  Installed: 0.6.25-1ubuntu5.1
  Candidate: 0.6.25-1ubuntu5.1
  Version table:
 *** 0.6.25-1ubuntu5.1 0
        500 http://us.archive.ubuntu.com karmic-updates/main Packages
        100 /var/lib/dpkg/status
     0.6.25-1ubuntu5 0
        500 http://us.archive.ubuntu.com karmic/main Packages