Watchdog flooded with "The directory sites/default is not writable"

Hi,

my site log is flooded with "The directory sites/default is not writable" message. I placed dpm('<pre>'. print_r(debug_backtrace(), 1) .'</pre>'); inside the function file_check_directory in the file.inc at line 121 and got this output at my frontpage:

 [0] => Array
        (
            [file] => /www/cgfplus_cz/public_html/sites/all/modules/image_resize_filter/image_resize_filter.module
            [line] => 418
            [function] => file_check_directory
            [args] => Array
                (
                    [0] => sites/default
                    [1] => 1
                )

        )

    [1] => Array
        (
            [file] => /www/cgfplus_cz/public_html/sites/all/modules/image_resize_filter/image_resize_filter.module
            [line] => 39
            [function] => image_resize_filter_process
            [args] => Array
                (
                    [0] => Array
                        (
                            [0] => Array
                                (
                                    [expected_size] => Array
                                        (
                                            [width] => 150
                                            [height] => 100
                                        )

                                    [actual_size] => Array
                                        (
                                            [width] => 1000
                                            [height] => 665
                                        )

                                    [add_properties] => Array
                                        (
                                            [width] => 
                                            [height] => 
                                        )

                                    [original] => /sites/default/files/content_images/miska_chlorella.JPG
                                    [location] => local
                                    [local_path] => sites/default/files/content_images/miska_chlorella.JPG
                                    [mime] => image/jpeg
                                    [extension] => jpg
                                )

... etc

I look in the imagefilter code and the problem is that drupal built-in function file_check_directory checks both that directory exists AND is writable (I'm not using Filefield CCK on this site). In the image_resize_filter module is that code:

   foreach ($folders as $folder) {
      $current_directory .= $folder .'/';
      $check_directory = $current_directory;
      // Use the "quiet" version of file_check_directory() provided by FileField
      // if it exists. This suppresses "Directory was created" messages.
      $file_check_directory = function_exists('field_file_check_directory') ? 'field_file_check_directory' : 'file_check_directory';
      $file_check_directory($check_directory, FILE_CREATE_DIRECTORY);
    }

So it seems that each folder in the whole path is checked to be writable - am I right? But keeping sites/default writable is a security hole, I have writable only /sites/default/temp and /sites/default/files. I think that code in this loop has to be changed to check only if the folder exists and check only the last one to be writable. Alternative approach to start "direcory checking loop" with the files directory, not with sites/ directory.