The helper function
_media_recursive_check_plain() is defined and used in media.browser.inc but is also used in media.media.inc. Unfortunately, it seems that media.browser.inc is not always loaded which can lead to errors, namely (when searching for files in the media browser):
Warning: array_walk_recursive() expects parameter 2 to be a valid callback, function '_media_recursive_check_plain' not found or invalid function name in media_query_media_browser_alter() (line 55 of /Users/devin/Sites/acquia-drupal/sites/all/modules/media/media.media.inc).
_media_recursive_check_plain() function should be moved out of media.browser.inc and into media.module where it will always be available.