Slim框架文件上传适用于POST，不适用于PUT

Question

I'm trying to upload a file to my Slim Framework server using PUT. I've successfully created a POST route where I can retrieve the uploaded file with no problem, but if I send the same request to the same route, with the only difference being the method, I receive a file from POST, null from PUT.

Here's my router:

            $app->put('/users/{id}', 'RideTimeServer\API\Controllers\UserController:update');
            $app->post('/users/{id}', 'RideTimeServer\API\Controllers\UserController:update'); // DEBUG:

And then the request is just passed through controller to processPicture method:

    protected function processPicture(Request $request): string
    {
        // First look for an uploaded picture
        if (!empty($request->getUploadedFiles()['picture'])) {
            // http://www.slimframework.com/docs/v3/cookbook/uploading-files.html
            $uploadedFile = $request->getUploadedFiles()['picture'];
            /**
             * { file, name, type }
             */
            var_dump($uploadedFile);
        // Then check URL
        } elseif (!empty($request->getParsedBody()['picture'])) {
            $url = $request->getParsedBody()['picture'];
            if (!filter_var($url, FILTER_VALIDATE_URL)) {
                throw new UserException('Invalid picture URL', 400);
            }
            var_dump($url);
        } else {
            // $this->container['logger']->addInfo('Submitted user with no picture');
            var_dump('Submitted user with no picture');
            var_dump($request->getUploadedFiles());
            var_dump($request->getParsedBody());
        }
        return '';
    }

Now if I send

curl -X PUT \
  http://localhost/ridetime/api/users/1 \
  -H 'Authorization: Bearer t0k3n' \
  -H 'cache-control: no-cache' \
  -H 'content-type: multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW' \
  -F 'picture=@/home/asdf/Tmp/Screenshot_20190125_005049.png'

i receive Submitted user with no picture, [] and null from the var_dump, yet if I change the request to POST:

curl -X POST \
  http://localhost/ridetime/api/users/1 \
  -H 'Authorization: Bearer t0k3n' \
  -H 'cache-control: no-cache' \
  -H 'content-type: multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW' \
  -F 'picture=@/home/asdf/Tmp/Screenshot_20190125_005049.png'

I get details of the uploaded file.

I tried replacing the -F 'picture=@...png with --upload-file ./file.png and the result was the same.