I'm running Ubuntu 12.04 with Gnome 3.4. I have two external hard drives. I encrypted both using Ubuntu's Disk Utility. When I use Nautilus to mount them, I'm asked for my decryption password. Regardless of whether I then click "Forget password immediately" or "Remember password until you logout", though, I find that Ubuntu does not lock the drives when I log out. Rather, when I log back in, they're still mounted.
(To be clear, restarting the computer does unmount them so that they require the password on the next log in.)
I'm concerned that these drives are remaining unprotected when I log out without restarting my computer. I would be grateful for help understanding whether this is a bug.