How to teach Thunar to mount flash drives?

Question

Gentoo

Thunar won't mount flash drives, with this message:

thunar-volman: Unsupported USB device

USE="mmx sse sse2 ssse3 sse4_1 cpudetection alsa X minimal bash-completion consolekit policykit dbus udev -joystick -gpm -bindist -debug -perl -llvm -fortran -java -http -ldap -themes -gstreamer -doc -qt -qt3support -qt4 -kde -gnome -cups -ipv6"

[ebuild   R    ] sys-apps/dbus-1.8.0  USE="X -debug -doc (-selinux) -static-libs -systemd {-test}" 0 kB
[ebuild   R    ] gnome-base/gvfs-1.18.3  USE="bluetooth cdda gtk udev udisks -afp -archive -avahi -bluray -fuse -gdu -gnome-online-accounts -gphoto2 -http -ios -libsecret -mtp -samba -systemd {-test}" 0 kB
[ebuild   R    ] xfce-base/thunar-1.6.3  USE="dbus exif libnotify pcre startup-notification udev -debug {-test}" XFCE_PLUGINS="trash" 0 kB
[ebuild   R    ] xfce-extra/thunar-volman-0.8.0  USE="libnotify -debug" 0 kB
[ebuild   R    ] sys-auth/polkit-0.112-r2  USE="gtk introspection nls pam -examples -jit -kde (-selinux) -systemd" 0 kB
[ebuild   R    ] sys-auth/consolekit-0.4.6  USE="acl pam policykit -debug -doc (-selinux) -systemd-units {-test}" 0 kB
[ebuild   R    ] xfce-extra/xfce4-notifyd-0.2.4  USE="-debug" 0 kB

Groups: wheel audio cdrom video cdrw usb users (is there a suspicion that I'm missing some group?)
xfce starts via slim, .xinitrc - I don't use it,
dbus and the whole zoo from consolekit, polkit, etc. are running (I have the ability to shutdown / restart the PC through the xfce menu. All buttons are active and NOT gray)
Advise where else to dig...