Yes -- this question has been asked before, but not answered. I have no "reputation" so I can't add to that thread. I can add that this is not limited to UPSes. I ran wireshark to see what was happening and Ubuntu does a snmp-get for three OIDs to the broadcast address.
1312 73.377595 172.16.254.109 255.255.255.255 SNMP 115 get-request 1.3.6.1.2.1.1.1.0 1.3.6.1.2.1.1.1.0 1.3.6.1.2.1.2.2.1.6.1
As the other thread states, analyzing syslog doesn't lead to any obvious answers.
Does anyone know why Ubuntu would be doing this?