Automount for flash drives now failing in 14.04

[MR ZenWiz]

I am running the following:

3.13.0-57-generic #95-Ubuntu SMP Fri Jun 19 09:28:15 UTC 2015 x86_64 GNU/Linux
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=14.04
DISTRIB_CODENAME=trusty
DISTRIB_DESCRIPTION="Ubuntu 14.04.3 LTS"

(actually Xubuntu...).

Two days ago, I noticed that when I insert my flash drives, they are
no longer automounted.

I thought it might be a boot problem, but I have rebooted a few times
since then for other reasons, and it still fails.

In order to get the system to recognize the drives as they are
normally mounted, I have to run Thunar and select the drive, then
everything works as I'd expect.

Here's what it looks like before I insert the drive:

mar at marbase:~ $ lsusb
Bus 002 Device 002: ID 8087:8001 Intel Corp.
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 002: ID 8087:8009 Intel Corp.
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 003 Device 002: ID 04a9:220e Canon, Inc. CanoScan N1240U/LiDE 30
Bus 003 Device 004: ID 046d:c517 Logitech, Inc. LX710 Cordless Desktop Laser
Bus 003 Device 005: ID 413c:2011 Dell Computer Corp. Multimedia Pro Keyboard
Bus 003 Device 003: ID 413c:1005 Dell Computer Corp. Multimedia Pro Keyboard Hub
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
mar at marbase:~ $ df
Filesystem      1K-blocks      Used Available Use% Mounted on
/dev/sda1        20811336   6323784  13407352  33% /
none                    4         0         4   0% /sys/fs/cgroup
udev              8050964         4   8050960   1% /dev
tmpfs             1612352      1216   1611136   1% /run
none                 5120         0      5120   0% /run/lock
none              8061756    101168   7960588   2% /run/shm
none               102400        32    102368   1% /run/user
/dev/sda4       927164968 709917984 207809816  78% /htera
/dev/sdb2       515930552 310808072 178891696  64% /home
/dev/sdb3      1375703508 620299800 685498912  48% /ttera

I insert the flash drive and lsusb sees it, but it never gets mounted
(notice the line of <<<...):

mar at marbase:~ $ lsusb
Bus 002 Device 002: ID 8087:8001 Intel Corp.
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 002: ID 8087:8009 Intel Corp.
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 003 Device 009: ID 0781:5506 SanDisk Corp. <<<<<<<<<<<<<<<<<<<
Bus 003 Device 002: ID 04a9:220e Canon, Inc. CanoScan N1240U/LiDE 30
Bus 003 Device 004: ID 046d:c517 Logitech, Inc. LX710 Cordless Desktop Laser
Bus 003 Device 005: ID 413c:2011 Dell Computer Corp. Multimedia Pro Keyboard
Bus 003 Device 003: ID 413c:1005 Dell Computer Corp. Multimedia Pro Keyboard Hub
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
mar at marbase:~ $ df
Filesystem      1K-blocks      Used Available Use% Mounted on
/dev/sda1        20811336   6323804  13407332  33% /
none                    4         0         4   0% /sys/fs/cgroup
udev              8050964         4   8050960   1% /dev
tmpfs             1612352      1264   1611088   1% /run
none                 5120         0      5120   0% /run/lock
none              8061756    102000   7959756   2% /run/shm
none               102400        32    102368   1% /run/user
/dev/sda4       927164968 709917984 207809816  78% /htera
/dev/sdb2       515930552 310807924 178891844  64% /home
/dev/sdb3      1375703508 620299800 685498912  48% /ttera

When I run Thunar, the drive shows up in the left column, and AFTER I
click on it, this shows in df:

mar at marbase:~ $ df
Filesystem      1K-blocks      Used Available Use% Mounted on
/dev/sda1        20811336   6323800  13407336  33% /
none                    4         0         4   0% /sys/fs/cgroup
udev              8050964         4   8050960   1% /dev
tmpfs             1612352      1264   1611088   1% /run
none                 5120         0      5120   0% /run/lock
none              8061756    102340   7959416   2% /run/shm
none               102400        32    102368   1% /run/user
/dev/sda4       927164968 709917984 207809816  78% /htera
/dev/sdb2       515930552 310808156 178891612  64% /home
/dev/sdb3      1375703508 620299800 685498912  48% /ttera
/dev/sdc1         4005028   3000364   1004664  75% /media/mar/MARTITAN

I have checked the Removable Drives and Media manager in the Settings,
and it shows "Mount removable drives when hot plugged" as checked, but
that's not what's happening.

Any advice?

Thanks.
MR