diff --git a/hgext/bookflow.py b/hgext/bookflow.py
--- a/hgext/bookflow.py
+++ b/hgext/bookflow.py
@@ -45,8 +45,10 @@
 
 def bookmarks_update(orig, repo, parents, node):
     if len(parents) == 2:
+        # called during commit
         return orig(repo, parents, node)
     else:
+        # called during update
         return False