The javac compiler incorrectly disallows access to members of protected
inner classes from classes belonging to a different package.

Consider the following two source files:

----------------
package a;

public class A {
    protected class In {
public void method() {
System.out.println("A.In.method called");
}
    }
}
----------------
import a.*;

public class B extends A {
    private class B_In extends A.In {
public void method() {
System.out.println("about to call super.method");
super.method();
}
    }

    public void callMethod() {
B_In bin = new B_In();
bin.method();
    }

    public static void main(String[] args) {
B b = new B();
b.callMethod();
    }
}
----------------

Compiling these two files induces the following error message:

. javac a/A.java B.java
B.java:7: The type a.A.In to which the member method belongs is not
    accessible from inner class B. B_In.
super.method();
^
1 error
.

Putting both files into the same package eliminates the problem.

I discovered this problem by trying to subclass
javax.swing.JTabbedPane.ModelListener as discussed in the comment preceding its
definition:
    /**
     * Subclasses that want to handle ChangeEvents differently
     * can override this to return a subclass of ModelListener or
     * another ChangeListener implementation.
     */
So the problem has practical impact.