USB key dmcrypt/LUKS, not properly unmounting

Binary package hint: hal

I have a 2GB USB key on which I have a single partition encrypted using dmcrypt/LUKS (cryptsetup). I have two separate Ubuntu machines in which I use this key (both Gutsy). BOTH machines have the exact same symptoms.
Here's the sequence of events:

1) Open Nautilus
2) Plug in USB key
3) Immediately, a new "place" appears in Nautilus, "Kingmax USB2.0"
4) I am prompted for a password, I supply it
5) The "place" in Nautilus now becomes USB_CRYPT
6) I use the key, everything works.
7) I right-click on USB_CRYPT and unmount
8) Immediately the "place" becomes "Kingmax USB2.0"
9) Remove USB key
10) The "place" in Nautilus disappears
(yes, so far everything is normal & happy)
11) Repeat steps 1-9
12) Now the place doesn't disappear. It still says "Kingmax USB2.0" even though the key is removed
13) Plug key back in
14) Nothing happens.
15) Right-click on "Kingmax USB2.0" and click on mount
16) Receive error:
"Cannot mount volume
Unable to mount the volume 'USB_CRYPT'.
v Details
mount: special device /dev/mapper/luks_crypto_f96d0ee5-dd93-4e72-861e-164f39f14771 does not exist"
17) Open command line, type "sudo cryptsetup luksOpen /dev/sdg1 usb_crypt_vol"
18) The "place" in Nautilus once again becomes USB_CRYPT and I can access the drive
19) I unmount the drive as before, and remove the key, and I'm back to where I was at step 12
20) Type "sudo cryptsetup luksClose usb_crypt_vol" to remove the mapper device
21) Repeat 13-19 and I'm actually back to where I started when I reboot (one good mount cycle, then bad mount cycle)

This happens EVERY time. And I feel like sometimes I run the cryptsetup luksOpen command and it doesn't auto-re-mount. I have added a script to my panel and to visudo so that I can run the commands manually without admin password, but it's quite annoying.

Is there any extra information I can provide to help diagnose/fix the problem?

-Casper