On investigation, the cause of this is that Files is launched from Plank using "pkexec" which resets the environment, not sudo. Unfortunately FIles crashes after the authentication dialog if this is simply changed to gksudo --preserve-env
On investigation, the cause of this is that Files is launched from Plank using "pkexec" which resets the environment, not sudo. Unfortunately FIles crashes after the authentication dialog if this is simply changed to gksudo --preserve-env