diff -u b/project_issue.module b/project_issue.module
--- b/project_issue.module
+++ b/project_issue.module
@@ -2813,10 +2813,16 @@
 function project_issue_issue_tag_autocomplete($vid, $tags_typed = '') {
   // Issues tag taxonomy vocabulary name
   $field_name = 'taxonomy_vocabulary_' . $vid;
-  // If the request has a '/' in the search text, then the menu system will have
-  // split it into multiple arguments, recover the intended $tags_typed.
+
+  // The menu system can send an unknown number of arguments if a '/' was in
+  // the search string.
   $args = func_get_args();
+
+  // The first argument is $vid. Remove it.
   unset($args[0]);
+
+  // If the menu system split the search into multiple arguments because '/' was
+  // part of the search, restore the original search.
   $tags_typed = implode('/', $args);
 
   // Make sure the field exists and is a taxonomy field.