Index: wp-includes/taxonomy.php
===================================================================
--- wp-includes/taxonomy.php	(revision 17357)
+++ wp-includes/taxonomy.php	(working copy)
@@ -879,7 +879,7 @@
 
 	if ( 'slug' == $field ) {
 		$field = 't.slug';
-		$value = sanitize_title($value);
+		$value = sanitize_title_for_query($value);
 		if ( empty($value) )
 			return false;
 	} else if ( 'name' == $field ) {
@@ -2824,7 +2824,12 @@
 		if ( is_int($term) ) {
 			$term = &get_term($term, $taxonomy);
 		} else {
-			$term = &get_term_by('slug', $term, $taxonomy);
+			$term_obj = &get_term_by('slug', $term, $taxonomy);
+
+			if ( !$term_obj || is_wp_error($term_obj) )
+				$term_obj = &get_term_by('name', $term, $taxonomy);
+
+			$term = &$term_obj;
 		}
 	}