which -a prints results twice

[Karl-Philipp Richter]

`which -a mount.cifs` prints

    /sbin/mount.cifs
    /sbin/mount.cifs

but should only print the entry once.

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: debianutils 4.4
Uname: Linux 4.0.1-040001-generic x86_64
ApportVersion: 2.17.2-0ubuntu1
Architecture: amd64
CurrentDesktop: Unity
Date: Sat May 9 21:23:16 2015
Dependencies:
 gcc-5-base 5.1~rc1-0ubuntu1
 libc6 2.21-0ubuntu4
 libgcc1 1:5.1~rc1-0ubuntu1
 multiarch-support 2.21-0ubuntu4
 sensible-utils 0.0.9
EcryptfsInUse: Yes
InstallationDate: Installed on 2015-04-02 (36 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Beta amd64 (20150326)
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: debianutils
SystemImageInfo:
 current build number: 0
 device name:
 channel: daily
 last update: Unknown
UpgradeStatus: No upgrade log present (probably fresh install)