External device mounted from the Desktop become unmounted?

[Andrew Robinson]

I have noticed twice now, that after mounting a device from the
auto-desktop icon that it becomes unmounted overtime and the icon will
never go away.

This has happened with my USB2.0 external hard drive and a USB thumb pen drive.

This last time what happened:
1) insert the thumb drive
2) right click on the "sdb1" icon & select mount (to /media/usbdisk)
3) went to lunch
4) came back and didn't show as being mounted
5) unplugged the device
6) the desktop icon is still there
7) plug the drive in again (icon doesn't change)
8) select mount again and get an error that there is no mount point
for /dev/sdb1

There is now way (to my knowledge) to remove the icon from the desktop
at this point without restarting XFCE.

Any ideas?