I have a remote Gentoo PC that stop automating USB drove. The only program I installed on it was "zenity" which should have nothing to do with auto-mount.
PC's are running XFCE and Setting Manager: Removable Drive and Media: first option is checked "ON" (mount removable media when Hot-plugged) When I insert USB the icon shows up on a desktop but it is not mounted. My home computer works OK, but remote PC stopped auto mounting after installing zenity.
