--- a/mercurial/copies.py	Sat Oct 01 20:20:11 2016 +0900
+++ b/mercurial/copies.py	Mon Oct 03 16:19:55 2016 +0200
@@ -465,6 +465,11 @@
     diverge = record all diverges in this dict
     copy = record all non-divergent copies in this dict
     fullcopy = record all copies in this dict
+
+    note: limit is only an optimization, and there is no guarantee that
+    irrelevant revisions will not be limited
+    there is no easy way to make this algorithm stop in a guaranteed way
+    once it "goes behind a certain revision".
     """
 
     ma = ca.manifest()