diff --git a/hgext3rd/fbamend/hiddenoverride.py b/hgext3rd/fbamend/hiddenoverride.py
--- a/hgext3rd/fbamend/hiddenoverride.py
+++ b/hgext3rd/fbamend/hiddenoverride.py
@@ -10,6 +10,7 @@
 import contextlib
 import os
 
+from mercurial.node import short
 from mercurial import (
     dispatch,
     error,
@@ -44,6 +45,7 @@
     unfi = repo.unfiltered()
     nodemap = unfi.changelog.nodemap
     offset = 0
+    result = []
     while True:
         node = content[offset:offset + 20]
         if not node:
@@ -51,8 +53,9 @@
         # remove unnecessary (non-obsoleted) nodes since pinnedrevs should only
         # affect obsoleted revs.
         if node in nodemap and unfi[node].obsolete():
-            yield node
+            result.append(node)
         offset += 20
+    return result
 
 def shouldpinnodes(repo):
     """get nodes that should be pinned: working parent + bookmarks for now"""
@@ -92,15 +95,21 @@
         fcntl.flock(lockfd, fcntl.LOCK_UN)
         os.close(lockfd)
 
-def savepinnednodes(repo, newpin, newunpin):
+def savepinnednodes(repo, newpin, newunpin, fullargs):
     # take a narrowed lock so it does not affect repo lock
     with flock(repo.svfs.join('obsinhibit.lock')):
-        nodes = set(loadpinnednodes(repo))
+        orignodes = loadpinnednodes(repo)
+        nodes = set(orignodes)
         nodes |= set(newpin)
         nodes -= set(newunpin)
         with util.atomictempfile(repo.svfs.join('obsinhibit')) as f:
             f.write(''.join(nodes))
 
+        desc = lambda s: [short(n) for n in s]
+        repo.ui.log('pinnednodes', 'pinnednodes: %r newpin=%r newunpin=%r '
+                    'before=%r after=%r\n', fullargs, desc(newpin),
+                    desc(newunpin), desc(orignodes), desc(nodes))
+
 def runcommand(orig, lui, repo, cmd, fullargs, *args):
     # return directly for non-repo command
     if not repo:
@@ -118,7 +127,7 @@
     newpin = set(n for n in newpin if unfi[n].obsolete())
     # only do a write if something has changed
     if newpin or newunpin:
-        savepinnednodes(repo, newpin, newunpin)
+        savepinnednodes(repo, newpin, newunpin, fullargs)
     return result
 
 def createmarkers(orig, repo, rels, *args, **kwargs):
diff --git a/tests/test-fbamend-hiddenoverride.t b/tests/test-fbamend-hiddenoverride.t
--- a/tests/test-fbamend-hiddenoverride.t
+++ b/tests/test-fbamend-hiddenoverride.t
@@ -1,9 +1,13 @@
   $ cat >> $HGRCPATH << EOF
   > [extensions]
+  > blackbox=
   > fbamend=$TESTDIR/../hgext3rd/fbamend
   > drawdag=$RUNTESTDIR/drawdag.py
   > [experimental]
   > evolution = all
+  > [blackbox]
+  > track = command, commandfinish, commandexception,
+  >   pinnednodes
   > EOF
 
   $ hg init
@@ -56,6 +60,37 @@
   |/
   @  0 A
   
+Check blackbox logs
+
+  $ hg blackbox -l 10000
+  *> debugdrawdag (glob)
+  *> pinnednodes: ['debugdrawdag'] newpin=[] newunpin=['112478962961'] before=[] after=[] (glob)
+  *> debugdrawdag exited 0 after * (glob)
+  *> log -G -T '{rev} {desc}\n' (glob)
+  *> log -G -T '{rev} {desc}\n' exited 0 after * (glob)
+  *> log -G -T '{rev} {desc}\n' --hidden (glob)
+  *> log -G -T '{rev} {desc}\n' --hidden exited 0 after * (glob)
+  *> update 1 --hidden -q (glob)
+  *> pinnednodes: ['update', '1', '--hidden', '-q'] newpin=['112478962961'] newunpin=[] before=[] after=['112478962961'] (glob)
+  *> update 1 --hidden -q exited 0 after * (glob)
+  *> update 0 -q (glob)
+  *> update 0 -q exited 0 after * (glob)
+  *> log -G -T '{rev} {desc}\n' (glob)
+  *> log -G -T '{rev} {desc}\n' exited 0 after * (glob)
+  *> prune 1 -q (glob)
+  *> pinnednodes: ['prune', '1', '-q'] newpin=[] newunpin=['112478962961'] before=['112478962961'] after=[] (glob)
+  *> prune 1 -q exited 0 after * (glob)
+  *> log -G -T '{rev} {desc}\n' (glob)
+  *> log -G -T '{rev} {desc}\n' exited 0 after * (glob)
+  *> bookmark -ir 1 BOOK --hidden -q (glob)
+  *> pinnednodes: ['bookmark', '-ir', '1', 'BOOK', '--hidden', '-q'] newpin=['112478962961'] newunpin=[] before=[] after=['112478962961'] (glob)
+  *> bookmark -ir 1 BOOK --hidden -q exited 0 after * (glob)
+  *> bookmark -d BOOK -q (glob)
+  *> bookmark -d BOOK -q exited 0 after * (glob)
+  *> log -G -T '{rev} {desc}\n' (glob)
+  *> log -G -T '{rev} {desc}\n' exited 0 after * (glob)
+  *> blackbox -l 10000 (glob)
+
 The order matters - putting bookmarks or moving working copy on non-obsoleted
 commits do not pin them. Test this using "debugobsolete" which will not call
 "createmarkers".