Compile-time error when using wildcard as type argument

A DESCRIPTION OF THE PROBLEM :
In the attached program, the compiler reports the following error (see Actual Result).
If we remove `? extends` from `? extends ClsA<Integer>` the program compiles.
Hence, `ClsA<Integer>` <: `ClsA<? super X>` when X equals `? extends Integer`.
Since `? extends ClsA<Integer>` <: `ClsA<Integer>`, I would expect the program to compile.
successfully.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
javac ClsA.java

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Compile
ACTUAL -
ClsA.java:15: error: type argument ? extends ClsA<Integer> is not within bounds of type-variable Y
  public final void foo(ClsB<? extends Integer, ? extends ClsA<Integer>> bar) {}
                                                ^
  where Y,X are type-variables:
    Y extends ClsA<? super X> declared in class ClsB
    X extends Object declared in class ClsB
1 error

---------- BEGIN SOURCE ----------
abstract class ClsA<M> {
  public ClsA() {}
}

class ClsB<X, Y extends ClsA<? super X>> {
  public ClsB() {
    super();
  }
}

class ClsC {
  public ClsC() {
    super();
  }
  public final void foo(ClsB<? extends Integer, ? extends ClsA<Integer>> bar) {}
}
---------- END SOURCE ----------

FREQUENCY : always