Quick tip: limit SNMP traps sent to a SNMP server
If you use multiple SNMP servers in your network, you might want to limit the traps each server receives. Configuring this functionality is easy: just list the traps you want a server to receive at the end of the snmp-server host configuration command.
When you specify the list of SNMP trap types a server should receive, a trap is sent to the server only if it’s listed in the snmp-server host command and enabled with the snmp-server enable traps command.
I also blogged a scenario showing what I found:
http://ccietobe.blogspot.com/2009/02/snmp-sending-traps-to-specific-hosts.html
Have you experienced this? Maybe just a bug in the IOS I was using, though I don't recall what version it was.