I'm also receiving a similar problem:
Nov 25 16:00:29 box1.example.com avahi-daemon[3310]: Received response with invalid source port 35558 on interface 'br0.0'
Nov 25 16:00:29 box1.example.com avahi-daemon[3310]: Invalid legacy unicast query packet.
Nov 25 16:00:29 box1.example.com avahi-daemon[3310]: Invalid legacy unicast query packet.
Nov 25 16:00:29 box2.example.com avahi-daemon[4616]: Invalid legacy unicast query packet.
Nov 25 16:00:29 box2.example.com avahi-daemon[4616]: Received response with invalid source port 35558 on interface 'eth0.0'
Nov 25 16:00:29 box2.example.com avahi-daemon[4616]: Invalid legacy unicast query packet.
Nov 25 16:00:29 box2.example.com avahi-daemon[4616]: Invalid legacy unicast query packet.
Nov 25 16:00:30 box1.example.com avahi-daemon[3310]: Received response with invalid source port 35558 on interface 'br0.0'
Nov 25 16:00:30 box1.example.com avahi-daemon[3310]: Received response with invalid source port 35558 on interface 'br0.0'
Nov 25 16:00:30 box2.example.com avahi-daemon[4616]: Received response with invalid source port 35558 on interface 'eth0.0'
Nov 25 16:00:30 box2.example.com avahi-daemon[4616]: Received response with invalid source port 35558 on interface 'eth0.0'
Nov 25 16:00:31 box1.example.com avahi-daemon[3310]: Received response with invalid source port 35558 on interface 'br0.0'
Nov 25 16:00:31 box2.example.com avahi-daemon[4616]: Received response with invalid source port 35558 on interface 'eth0.0'
Nov 25 16:00:32 box1.example.com avahi-daemon[3310]: Received response with invalid source port 35558 on interface 'br0.0'
Nov 25 16:00:32 box2.example.com avahi-daemon[4616]: Received response with invalid source port 35558 on interface 'eth0.0'
Nov 25 16:00:33 box1.example.com avahi-daemon[3310]: Received response with invalid source port 35558 on interface 'br0.0'
Nov 25 16:00:33 box2.example.com avahi-daemon[4616]: Received response with invalid source port 35558 on interface 'eth0.0'
I'm also receiving a similar problem:
Nov 25 16:00:29 box1.example.com avahi-daemon[3310]: Received response with invalid source port 35558 on interface 'br0.0'
Nov 25 16:00:29 box1.example.com avahi-daemon[3310]: Invalid legacy unicast query packet.
Nov 25 16:00:29 box1.example.com avahi-daemon[3310]: Invalid legacy unicast query packet.
Nov 25 16:00:29 box2.example.com avahi-daemon[4616]: Invalid legacy unicast query packet.
Nov 25 16:00:29 box2.example.com avahi-daemon[4616]: Received response with invalid source port 35558 on interface 'eth0.0'
Nov 25 16:00:29 box2.example.com avahi-daemon[4616]: Invalid legacy unicast query packet.
Nov 25 16:00:29 box2.example.com avahi-daemon[4616]: Invalid legacy unicast query packet.
Nov 25 16:00:30 box1.example.com avahi-daemon[3310]: Received response with invalid source port 35558 on interface 'br0.0'
Nov 25 16:00:30 box1.example.com avahi-daemon[3310]: Received response with invalid source port 35558 on interface 'br0.0'
Nov 25 16:00:30 box2.example.com avahi-daemon[4616]: Received response with invalid source port 35558 on interface 'eth0.0'
Nov 25 16:00:30 box2.example.com avahi-daemon[4616]: Received response with invalid source port 35558 on interface 'eth0.0'
Nov 25 16:00:31 box1.example.com avahi-daemon[3310]: Received response with invalid source port 35558 on interface 'br0.0'
Nov 25 16:00:31 box2.example.com avahi-daemon[4616]: Received response with invalid source port 35558 on interface 'eth0.0'
Nov 25 16:00:32 box1.example.com avahi-daemon[3310]: Received response with invalid source port 35558 on interface 'br0.0'
Nov 25 16:00:32 box2.example.com avahi-daemon[4616]: Received response with invalid source port 35558 on interface 'eth0.0'
Nov 25 16:00:33 box1.example.com avahi-daemon[3310]: Received response with invalid source port 35558 on interface 'br0.0'
Nov 25 16:00:33 box2.example.com avahi-daemon[4616]: Received response with invalid source port 35558 on interface 'eth0.0'
box1:
Package: avahi-daemon
State: installed
Automatically installed: yes
Version: 0.6.23-4ubuntu4
box2:
Package: avahi-daemon
State: installed
Automatically installed: yes
Version: 0.6.23-2ubuntu2.1
Please let me know if I can provide any additional information that may be of use.