Firebase x-http-method-override parameter is ignored

HTTP POST requests using are ?x-http-method-override=PATCH

treated as POST instead of PATCH calls in the Firebase REST API. This has started to happen over the past two weeks.

The Firebase documentation still mentions this setting, isn't it more accurate or is it a bug in Firebase?

The concrete (Java) code works in Google Appengine where PATCH is not directly supported. (Overcoming App Engine Compatible Firebase SDK)

For reference, the request is executed with the following code, the response indicates a successful request without any errors.

HttpRequestFactory requestFactory = HTTP_TRANSPORT.createRequestFactory(new 
HttpRequestInitializer() {
    @Override
    public void initialize(HttpRequest request) {
        request.setParser(new JsonObjectParser(JSON_FACTORY));
    }
});
String path = url+".json"+"?x-http-method-override=PATCH";
GenericUrl fullUrl = new GenericUrl(path);

JsonHttpContent content = new JsonHttpContent(JSON_FACTORY, data);
content.setMediaType(new HttpMediaType("application/json; charset=UTF-8"));
HttpRequest request = requestFactory.buildPostRequest(fullUrl,content);
HttpResponse response = request.execute();