pbuilder/cowbuilder and piuparts failed

Today, I've failed to create pbuilder's base.tgz and cowbuilder's base.cow, and log says as below

Get:1 http://ftp.jp.debian.org sid Release.gpg [836 B]
Hit http://ftp.jp.debian.org sid Release
Ign http://ftp.jp.debian.org sid Release
Hit http://ftp.jp.debian.org sid/main amd64 Packages/DiffIndex
Hit http://ftp.jp.debian.org sid/main Translation-en
Fetched 836 B in 0s (3011 B/s)
Reading package lists...
W: GPG error: http://ftp.jp.debian.org sid Release: The following signatures were invalid: BADSIG AED4B06F473041FA Debian Archive Automatic Signing Key (6.0/squeeze) 
I: Obtaining the cached apt archive contents

 "The following signatures were invalid: BADSIG" ?

apt (0.9.7.8) unstable; urgency=criticial
 
  * SECURITY UPDATE: InRelease verification bypass
    - CVE-2013-1051
   
  [ David Kalnischk ]
  * apt-pkg/deb/debmetaindex.cc,
    test/integration/test-bug-595691-empty-and-broken-archive-files,
    test/integration/test-releasefile-verification:
    - disable InRelease downloading until the verification issue is
      fixed, thanks to Ansgar Burchardt for finding the flaw

Maybe this cause it (just wild guess).

And piuparts also failed.

8m16.5s DEBUG: Starting command: ['chroot', '/tmp/tmpivurbJ', 'eatmydata', 'umount', '/proc']
8m16.5s DUMP: 
  umount: /proc: device is busy.
          (In some cases useful info about processes that use
           the device is found by lsof(8) or fuser(1))
8m16.5s DEBUG: Command failed (status=1), but ignoring error: ['chroot', '/tmp/tmpivurbJ', 'eatmydata', 'umount', '/proc']
8m16.5s DEBUG: Starting command: ['rm', '-rf', '--one-file-system', '/tmp/tmpivurbJ']
8m16.6s DUMP: 
  rm: skipping '/tmp/tmpivurbJ/proc', since it's on a different device
8m16.6s ERROR: Command failed (status=1): ['rm', '-rf', '--one-file-system', '/tmp/tmpivurbJ']
  rm: skipping '/tmp/tmpivurbJ/proc', since it's on a different device
  
8m16.7s DEBUG: Starting command: ['chroot', '/tmp/tmpivurbJ', 'umount', '/proc']
8m16.8s DUMP: 
  chroot: failed to run command 'umount': No such file or directory

It mounts binfmt_misc mount under /proc and try to umount /proc without umount it again, again and again... then failed. What causes this annoying behavior?

Please let me know.