javac improperly complains of conflict with non-inherited method

The folowing is an original test case to catch the problem
detected by jacks 8.1.1.1-default-abstract-12

==================== A.java ====================
/*
 * @test %W% %E%
 * @bug 4738690
 * @summary javac improperly complains of conflict with non-inherited method
 * @author gafter
 *
 * @compile A.java B.java
 */

package a;
public abstract class A {
    abstract void f();
}
==================== B.java ====================
interface B {
    int f();
}

/** C is legal because no two *inherited* methods conflict. a.A.f() is
 * not inherited because it is package private in another package. */
abstract class C extends a.A implements B {
}