Long paths are not handled correctly when deleting partition mappings

The bug seems to be in kpartx and long path handling
sergiusens@lindon:~/source/launchpad.net/snapcraft$ cd /
sergiusens@lindon:/$ sudo kpartx -avs ^C
sergiusens@lindon:/$ sudo losetup -a
[sudo] password for sergiusens:
sergiusens@lindon:/$ sudo kpartx -avs /home/sergiusens/source/launchpad.net/snapcraft/examples/godd/images/15.04.img
add map loop0p1 (252:0): 0 8192 linear /dev/loop0 8192
add map loop0p2 (252:1): 0 131072 linear /dev/loop0 16384
add map loop0p3 (252:2): 0 2097152 linear /dev/loop0 147456
add map loop0p4 (252:3): 0 2097152 linear /dev/loop0 2244608
add map loop0p5 (252:4): 0 3272704 linear /dev/loop0 4341760
sergiusens@lindon:/$ sudo losetup -a
/dev/loop0: [2050]:7872194 (/home/sergiusens/source/launchpad.net/snapcraft/examples/godd/images/15.04.img)
sergiusens@lindon:/$ sudo kpartx -ds /home/sergiusens/source/launchpad.net/snapcraft/examples/godd/images/15.04.img
sergiusens@lindon:/$ sudo losetup -a
/dev/loop0: [2050]:7872194 (/home/sergiusens/source/launchpad.net/snapcraft/examples/godd/images/15.04.img)

What follows is the snapcraft specific report
When I run snapcraft run, it boots the snappy kvm but leaves two loop devices behind:

$ losetup -a
/dev/loop0: []: (/home/elopio/workspace/canonical/snapcraft/trunk/examples/downloader-with-wiki-parts/image/15.04.img)
/dev/loop1: []: (/home/elopio/workspace/canonical/snapcraft/trunk/examples/downloader-with-wiki-parts/image/15.04.img)

Tested in vivid and wily

To reproduce:
bzr branch lp:snapcraft
cd snapcraft
cd examples/downloader-with-wiki-parts
./../../bin/snapcraft assemble
./../../bin/snapcraft run

$ apt-cache policy ubuntu-device-flash
ubuntu-device-flash:
  Instalita: 0.31-0ubuntu1
  Kandidato: 0.31-0ubuntu1
  Version table:
 *** 0.31-0ubuntu1 0
        500 http://ppa.launchpad.net/snappy-dev/tools-proposed/ubuntu/ vivid/main amd64 Packages
        500 http://ppa.launchpad.net/snappy-dev/tools/ubuntu/ vivid/main amd64 Packages
        100 /var/lib/dpkg/status
     0.20-0ubuntu1 0
        500 http://cr.archive.ubuntu.com/ubuntu/ vivid/universe amd64 Packages