sorry for spamming the list today. @Dan you have probably read this already:
https://stackoverflow.com/questions/41231270/econnrefused-errors-on-udp-sendtoturns out that at least on my system (Windows 7) [netsend -u] only closes the socket when sending to a non-reachable port on *localhost*. sending to any other (existing or non-existing) host won't close the socket. this means that there's even less reason to consider this a feature and I'm not sure if there are really any patches out there which depend on this behaviour.
Christof