Jersey: @Consumes doesn't quite work when content-type is not set

I'm trying to figure out how @Consumes works here.

I have a simplified resource that looks like the below, and I only want this resource to consume "application/vnd.myApp+xml".

@Path("/app")
@Consumes("application/vnd.myApp+xml")
@Produces("application/vnd.myApp+xml")
public class AppResource {
    @POST
    public Response postStuff() {
        ...
    }
}

I have the following testcases:-

public class AppResourceTest extends JerseyTest {
    @Test
    public void testApp() {
        // #1: Works fine
        ClientResponse response = resource().path("app")
                    .accept("application/vnd.myApp+xml")
                    .post(ClientResponse.class);

        ...

        // #2: Throws a 415 Unsupported Media Type
        ClientResponse response = resource().path("app")
                    .accept("application/vnd.myApp+xml")
                    .type("text/plain")
                    .post(ClientResponse.class);

        ...

        // #3: Works fine
        ClientResponse response = resource().path("app")
                    .accept("application/vnd.myApp+xml")
                    .type("application/vnd.myApp+xml")
                    .post(ClientResponse.class);

        ...
    }
}

From the 3 tests above, #2 and #3 work as expected.

As for #1, if I don't set the content-type, why doesn't it throw a 415 too?