Thanks, relaunching Finder refreshed the list.
This was a Finder bug that I hadn't ever seen before, despite some of its annoying anomalies. On the other hand, there are lots of bugs in lots of OS X backup utilities, so seeing this caused a bit of consternation.
Request: Please document this problem in a "Troubleshooting" section in SuperDuper user guide...
Thanks!
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BUY VAPORIZERS