cobertura fails to include interface compiled class

[RamyaR94]

Hi,
Following is my war and instrument task in ant

    <target name="coberturacompile" >
        <javac destdir="build/classes" debug="true" srcdir="src">
            <classpath refid="compile.classpath"/>
            <classpath refid="cobertura.classpath" />
        </javac>
    </target>

    <target name="instrument" depends="coberturacompile">
            <cobertura-instrument datafile="cobertura.ser" todir="${instrumented.dir}">
                       <ignore regex="org.slf4j.*" />
                       <fileset dir="${classes.dir}">
                          <include name="**/*.class" />
                          <exclude name="**/*Test.class" />
                      </fileset>
            </cobertura-instrument>
    </target>
    <target name="warinst" depends="instrument">
        <war destfile="dist/cober.war" webxml="web/WEB-INF/web.xml">
            <fileset dir="web"/>
            <lib dir="web/WEB-INF/lib"/>
            <classes dir="build/instrumented"/>
        </war>
        <copy file="dist/cober.war" todir="${local.deploy}"/>
     </target>

I have a interface but i am not able to find that compiled class in my cober.war. So in runtime the server throws an exception and able to instrument the classes which implements an interface. The issue is only when an interface is implemented. please help me with a solution as soon as possible. Cobertura version is 2.1.1