Custom object deserializes fine in Jax-RS but if it is used in another object it doesn't work

Deserializing works fine if I just pass my custom object through

@POST
public Response saveCustomObject(CustomObject data)
{
    // Prints correct value
    System.out.println(data);
}

However, if it is a property on another object, it just gets the default value of my custom object

@POST
public Response saveCustomObjectWrapper(CustomObjectWrapper data)
{
    // Prints incorrect value
    System.out.println(data.getCustomObject());
}

My provider is registered and looks like this:

public CustomObject readFrom(Class<CustomObject> type, Type type1, Annotation[] antns, MediaType mt, MultivaluedMap<String, String> mm, InputStream in) throws IOException, WebApplicationException
{
    try {
        return new CustomObject(IOUtils.toString(in));
    } catch (Exception ex) {
        throw new ProcessingException("Error deserializing a CustomObject.", ex);
    }
}