Netcat anomaly

[CLOSE Dave]

I have a Fedora 20 machine which is receiving UDP broadcast packets at
regular intervals on a strange high port. No program is presently
listening for these packets. If I run, "tcpdump -i eth0 port 29531", I
see each of the packets arriving just as I expect. Note, the packets are 
not empty and contain mostly ASCII characters.

But if I then run, "nc -lu 29531", I don't see anything! Why not? What
obvious thing am I missing?

This same operation works better (but still not as I expect) on Fedora 
14. NC shows one packet arriving but then doesn't show any more.

Running NC under strace on both machines, I see F14 NC seems to use 
poll(2). It outputs one packet then hangs on poll. F20 NC seems to use 
select(2). It hangs on the first call.

SELinux and the firewall are disabled on both machines.
-- 
Dave Close