pdftk fails to open an encrypted file

This bug is similar to https://bugs.launchpad.net/ubuntu/+source/pdftk/+bug/1191381 , although unrelated to AES as far as I undestand.

I have an encrypted file that pdftk fails to open even if a correct owner/user/input password is provided. Here's a sample command.
$ pdftk file.pdf output file2.pdf user_pw pdftkpassword
Error: Failed to open PDF file:
   file.pdf
   OWNER OR USER PASSWORD REQUIRED, but not given (or incorrect)
Errors encountered. No output created.
Done. Input errors, so no output created.

Same issue doesn't happen with qpdf or pdfinfo. The file is copyrighted - it's an electronic version of a local newspaper - but I could share it privately.

Here's some info on the file and pdftk package.

$ pdfinfo file.pdf -upw some_password
Producer: iText 2.1.7 by 1T3XT
CreationDate: Tue Jun 2 03:50:27 2015
ModDate: Tue Jun 2 12:32:26 2015
Tagged: no
UserProperties: no
Suspects: no
Form: none
JavaScript: no
Pages: 32
Encrypted: yes (print:yes copy:no change:no addNotes:no algorithm:RC4)
Page size: 892.913 x 1332.28 pts
Page rot: 0
File size: 12742195 bytes
Optimized: no
PDF version: 1.4

$ lsb_release -rd
Description: Ubuntu 15.04
Release: 15.04
$ sudo apt-get policy pdftk
pdftk:
  Installed: 2.02-2
  Candidate: 2.02-2
  Version table:
 *** 2.02-2 0
        500 http://archive.ubuntu.com/ubuntu/ vivid/universe amd64 Packages
        100 /var/lib/dpkg/status