diff -u b/core/includes/common.inc b/core/includes/common.inc
--- b/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -7306,7 +7306,11 @@
  *   themes).
  * - Updates the bootstrap flag for modules implementing bootstrap_hooks().
  * - Rebuilds the full database schema information (invoking hook_schema()).
- * - Rebuilds data structures of all modules (invoking hook_rebuild()).
+ * - Rebuilds data structures of all modules (invoking hook_rebuild()). In
+ *   core this means
+ *   - blocks, node types, date formats and actions are synchronized with the
+ *     database
+ *   - The 'active' status of fields is refreshed.
  * - Rebuilds the menu router.
  *
  * This means the entire system is reset so all caches and static variables are