Ok, so it isn't a problem, other than making the logs usless to look at?
I'm not sure if that is something that can be fixed in the package or not. It appears to be it's normal MO, so it just spams the logs.
The real log file might contain more useful info. From the console, you could always run a command like this:clog -f /var/log/system.log | grep -v promisc
And monitor that way for suspicious entries.