We find a bug in NormalDistributionImpl

[rakesh]

                                                                                
    <%@ page import 
="org.apache.commons.math.distribution.NormalDistributionImpl" %>
<%
        //double p=0;
        //double p=0.5;
        //double p=1;
        double p=0.4;
        NormalDistributionImpl  nd = new NormalDistributionImpl(50,5);
        double icp = nd.inverseCumulativeProbability(p);
        out.println(icp);
%>

why the above programme does not work for p=0.4? 
                 Rakesh.P    &   SathyaJothi.A