It means that it’s receiving queries on interfaces other than the interface that it’s advertised on. Multihomed box, maybe?
If it is a multihome problem, you can try and force which interface it binds to using the “interface” configuration option. It may or may not work, though, as I don’t have a multi-homed machine to try it on, nor a solaris machine, obviously.
Disappearing machine is probably related. If it’s ignoring mdns queries, it will eventually drop off iTunes (and soundbridge).
Probably the best solution would be to use howl as a mdns responder, and compile with “–enable-howl –with-howl-includes=/usr/local/howl-0.9.8” (or whatever).