Index: wp-includes/taxonomy.php
===================================================================
--- wp-includes/taxonomy.php	(revision 17230)
+++ wp-includes/taxonomy.php	(working copy)
@@ -1948,7 +1948,10 @@
 		}
 	}
 
-	if ( $term_id = term_exists($slug) ) {
+	$term_id = term_exists($slug);
+	$other_tax_exists = $wpdb->get_var( $wpdb->prepare( "SELECT taxonomy FROM $wpdb->term_taxonomy WHERE term_id = %d", $term_id ) );
+	
+	if ( $term_id && !$other_tax_exists ) {
 		$existing_term = $wpdb->get_row( $wpdb->prepare( "SELECT name FROM $wpdb->terms WHERE term_id = %d", $term_id), ARRAY_A );
 		// We've got an existing term in the same taxonomy, which matches the name of the new term:
 		if ( is_taxonomy_hierarchical($taxonomy) && $existing_term['name'] == $name && $exists = term_exists( (int) $term_id, $taxonomy ) ) {