Suppose there are 2 users foo & bar. foo logs in and the external usb disk is auto-mounted under /media/foo/... . Now foo logs out and bar logs in. The disk is still mounted under /media/foo/... and as a consequence clicking on the unity-launcher for that disk icon launches gedit instead of nautilus (or 'Files' - whatever you want to call it) with an error message which is of course 'don't have permissions etc etc'...I've had this problem since 12.10 if I'm not mistaken...
ProblemType: Bug
DistroRelease: Ubuntu 13.10
Package: gvfs 1.18.2-0ubuntu1
ProcVersionSignature: Ubuntu 3.11.0-12.19-generic 3.11.3
Uname: Linux 3.11.0-12-generic x86_64
NonfreeKernelModules: fglrx
ApportVersion: 2.12.5-0ubuntu2
Architecture: amd64
Date: Mon Oct 21 17:52:50 2013
MarkForUpload: True
SourcePackage: gvfs
Symptom: storage
Title: Documents cannot be opened in desktop UI on storage device
UpgradeStatus: Upgraded to saucy on 2013-10-20 (1 days ago)
Status changed to 'Confirmed' because the bug affects multiple users.