--- a/mercurial/cmdutil.py	Tue Jun 30 22:36:49 2015 -0700
+++ b/mercurial/cmdutil.py	Tue Jun 30 22:39:28 2015 -0700
@@ -2614,6 +2614,8 @@
                 if bms:
                     marks = repo._bookmarks
                     for bm in bms:
+                        ui.debug('moving bookmarks %r from %s to %s\n' %
+                                 (marks, old.hex(), hex(newid)))
                         marks[bm] = newid
                     marks.recordchange(tr)
             #commit the whole amend process