Lacie Won't Unmount - Applications Running

[gmachen]

Hold the presses! It just unmounted.

But then I mounted the two partitions again in Disk Utility, and now I'm back to the same behavior: the data-only partition will unmount, but the bootable backup won't.

Chain of events:
- I had launched SD! as root and scheduled a Smart Update for five minutes later.
- I logged-out.
- Five minutes later SD! duly came up behind the login window and did the backup. (It was doing the backup as root.)
- I logged into my regular Admin account, and then I got the bootable backup partition to unmount from the Finder.
- I was so surprised that I promptly launched Disk Utility and re-mounted the two partitions.
- Now, as before, the data partition will unmount but the bootable backup partition will not unmount, complaining that it is "in use."

Does this provide a clue to anybody?