ProxyMetaClass and Interceptor: some calls are not intercepted

class A{
   void a(){ b() }
   void b(){}
}

   benchmarkInterceptor = new BenchmarkInterceptor()
   proxy = ProxyMetaClass.getInstance(A.class)
   proxy.setInterceptor(benchmarkInterceptor)
   proxy.use {
        a = new A()
        a.a()
        a.b()
   }
      
stats = benchmarkInterceptor.statistic()
stats.each{
   println ""
   it.each{ print it+" "}
} 

b 1 0 
ctor 1 0 
a 1 0