Well I have heard of this scaner and used it before and not have this problem.
However, I don't recomend using a ICMP based scanner for networks, I recomend using ARP based scanning.
Now, ettercap is one of the most popular programs to use ARP scanning, however it's unstable on windows based systems. I use Cain & Able from www.oxid.it
to scan networks for hosts. The downside to ARP sniffers is that they ONLY can detect computers upto the router, but every computer HAS TO respond to ARP packets.
So with ARP scanning, if you have a network that has many routers, it's bad to use. However with default configuration, routers will pass ICMP traffic.