Why does a hidden static method compile under Sun JDK 6 but cause a compile failure under OpenJDK 6 and 7?

The following class:

public class StaticMethodsDemo {

    public static class A {
        public static A make() { return new A(); };
    }
    public static class B extends A {
        public static B make() { return new B(); };
    }
    public static class BPrime<T> extends A {
        public static <T> BPrime<T> make() { return new BPrime<T>(); };
    }

    public static void main(String[] args) {
        B.make();
        // compiles under Sun JDK 1.6.0_20 but fails under Oracle JDK 1.7.0_01. Why?
        BPrime.<Object>make();
    }
}

compiles under Sun JDK 1.6.0_20 (Windows 64-bit, but shouldn't make a difference) but fails under Oracle JDK 1.7.0_01 (same platform) and OpenJDK 1.6.0_20 (Ubuntu) [1] with:

[ERROR] StaticMethodsDemo.java:[37,14] error: reference to make is ambiguous, both method make() in A and method <T>make() in BPrime match

Why? How does the generic parameter (which should be erased, no?) cause this apparent mismatch. Note that removing generics as follows:

...
public static class BPrime<T> extends A {
    T val;
    public static BPrime<?> make() { return new BPrime<Object>(); };
    public void setT(T val) { this.val = val; }
}

public static void main(String[] args) {
    B.make();
    BPrime<Long> bprime = (BPrime<Long>) BPrime.make();
    bprime.setT(Long.valueOf(10));
}

compiles and runs too (so the generics hack doesn't cause any weird runtime casting errors).

Issue 461: jclouds-core compilation fails using stock ubuntu openjdk