Tags/categories import fail

On a clean Drupal install, I attempted to migrate my Wordpress blog. I did it via the UI first and received some incomprehensible errors, and afterwards attempted it via Drush, and receieved some better errors:

server:/drupal# drush mi --all
achtonnetBlogEntry addFieldMapping: field_tags was previously mapped, overridden    [warning]
Imported 1 in 0.1 sec (837/min) - done with 'achtonnetAuthor'                       [completed]
Imported 21 in 0.7 sec (1842/min) - done with 'achtonnetCategory'                   [completed]
Imported 3 in 0.2 sec (1479/min) - done with 'achtonnetTag'                         [completed]
array_diff(): Argument #1 is not an array                                           [error]
File /drupal/modules/wordpress_migrate/wordpress_item.inc, line 767
array_diff(): Argument #1 is not an array                                           [error]
File /drupal/modules/wordpress_migrate/wordpress_item.inc, line 767
array_diff(): Argument #1 is not an array                                           [error]
File /drupal/modules/wordpress_migrate/wordpress_item.inc, line 767
[...]
Imported 1 in 4.5 sec (1623/min) - done with 'achtonnetBlogEntry'                   [completed]
Imported 9 in 2.1 sec (257/min) - done with 'achtonnetPage'                         [completed]
Imported 28 in 5.4 sec (313/min) - done with 'achtonnetAttachment'                  [completed]
No node ID provided for comment                                                     [error]
No node ID provided for comment                                                     [error]
No node ID provided for comment                                                     [error]
[...]
Imported 0 in 2.2 sec (2163/min) - done with 'achtonnetComment'                     [completed]

This was my fix, though I am unsure of how correct it is:

diff --git a/wordpress_item.inc b/wordpress_item.inc
index 48e095d..da6199a 100644
--- a/wordpress_item.inc
+++ b/wordpress_item.inc
@@ -764,7 +764,7 @@ abstract class WordPressItemMigration extends WordPressMigration {
               }
             }
           }
-          $diff = array_diff($row->$value_name, $done_terms);
+          $diff = array_diff((array) $row->$value_name, $done_terms);
           foreach ($diff as $new_term_name) {
             // Let's see if the term already exists
             $matches = taxonomy_term_load_multiple(array(),

NB: This seems to only fix it when using Drush.