ultramonkey real server problem

i am trying to use ultramonkey and encountered a problem.
if i set up more than 2 real servers, ultramonkey only sticks with one
of them. If only 1 or 2 real servers it works fine. Anybody knows why?
Thanks ahead.
following is my ldirectord.cf
# Configuration file: ldirectord.cf
checktimeout=10
checkinterval=2
fallback=127.0.0.1:80
autoreload=no
logfile="/var/log/ldirectord.log"
quiescent=yes

#
virtual=192.168.0.210:80
fallback=127.0.0.1:80
real=192.168.0.201:80 masq
real=192.168.0.202:80 masq
real=192.168.0.203:80 masq
service=http
request="index.html"
receive="Test Page"
scheduler=rr
protocol=tcp
checktype=negotiate