javac treats inherited abstract method as an overrider

javac improperly rejects this program (detected by jacks 8.4.6.4-abstract-7)

/*
 * @test %W% %E%
 * @bug 4717181
 * @summary javac treats inherited abstract method as an overrider
 * @author gafter
 *
 * @compile T4717181a.java
 */

class T4717181a {
    abstract class C {
        abstract void m();
    }
    interface I {
        void m();
    }
    abstract class D extends C implements I {}
}


and this

/*
 * @test %W% %E%
 * @bug 4717181
 * @summary javac treats inherited abstract method as an overrider
 * @author gafter
 *
 * @compile T4717181b.java
 */

class T4717181b {
    static class E1 extends Exception {}
    static class E2 extends Exception {}
    static class E3 extends Exception {}
    static abstract class Ta {
        public abstract void m() throws E1, E2;
    }
    interface Tb {
        void m() throws E2, E3;
    }
    static abstract class Tc extends Ta implements Tb {
        {
            try {
                m(); // intersect throws clauses
            } catch (E2 e2) {
            }
        }
    }
}