strange choice of method

[Stephan Herrmann]

In the following code javac raises exactly one error:

//--------------
public class X {
         void a() {}
         private static void a(String s) {}
         private void c() {}
         private static void c(String s) {}
         static class M1 extends X {
                 public void x() {
                         a(null);
                         c(null);
                 }
         }
         static class M2 {
                 public void x() {
                         a(null);
                         c(null);
                 }
         }
}
//----------------

The first call "a(null)" is rejected, because the no-arg instance method is 
selected, whereas the second such call is accepted, targeting the static method.

Also both calls "c(null)" are accepted.

Is there any intention behind this?

thanks,
Stephan

PS: These observations hold for version 5 through 25 ea. javac 1.4 actually 
accepts the program. Not sure if it helps understanding the why of it.