Type inference more restrictive in JDK 7 than JDK 6?

I think this might be related to Why does a generic cast of a List<? extends Set..> to List<Set..> succeed on Sun JDK 6 but fail to compile on Oracle JDK 7?

If we take the following classes, they compile fine under JDK 6:

public final class Foo<V> {

    private final V value;

    private Foo(final V value) {

        this.value = value;
    }

    public static <T, R extends T> Foo<T> of(final R value) {

        return new Foo<T>(value);
    }
}

final class Tester {

    @Test(groups="unit")

    public static void test() {

        bar(Foo.of(BigDecimal.ZERO));  // This line fails in JDK 7 but not JDK 6
    }

    private static void bar(final Foo<? extends Number> target) {

        assert target != null;
    }
}

However, under JDK 7, I receive the following error:

[ERROR] \work\fsb-core\src\test\java\com\fsb\core\Foo.java:[42,8] error:
              method bar in class Tester cannot be applied to given types;

I thought type inference was less restrictive (e.g., adding constructor inference) in JDK 7. However, here, the compiler is rejecting a type that is valid under JDK 6.

Is this a bug? Or were the rules on inference made more stringent for methods?