[rik17]

This bug is relatively obscure but nonetheless problematic until understood:

- Setup an automated script to backup unattended disk1 to disk2
- Have a disk3 that's mounted and use it to manually backup something from disk1 to disk3. Quit SD when disk3 is selected in the target popup. (That's what is important)
- Then unmount disk3 from the finder.

Now when the automated script wants to run, it'll fail. SD will quit unexpectedly and the applescripts will stop with an error.

The workaround is to open SD manually, click "cancel" on the alert box that says that disk3 is unavailable, select another disk from the target popup (which is blank by then), do a small backup and then quit SD. Now SD won't complain about disk3 being missing.