When you try "yphelper --map server" , it doesn't answer you so "ypint -s
server", doesn't work.
I have all the oficial patches for the nis tools.
ypbind-3.3-24
yp-tools-2.3-2
ypserv-1.3.9-1

if you modify the ypinit script to set $map by hand to the maps you want
to  share, every thing works fine, the slave server works. It works when
the master goes down and it accepts the yppushes from the master server.