Jeff, for clusters, I'd expect that you would only be seeing this message on the 'active' cluster member on any clusters you have setup.
So, when you say you don't see this message on the other controllers, are these other controllers 'Primary' active cluster members too?
What version of WiNG?
Something that I'm curious about is the out "New member 19.F9.5C.43 standby load 8" Can you confirm that the MiNT ID 19.F9.5C.43 is the correct MiNT ID for the cluster member? The "New" part of this message is what's throwing me.
Can you run these and post the results for this particular cluster?
show cluster configuration (on both cluster members)
show cluster status (on both cluster members)
show cluster history (on the controller generating these messages)