When you hit the Add button while nothing is selected (or there are no SFS files in the required dir) it creates a non-empty "empty" sfstray_list, and when you hit Apply it sends all writable mounted media down the toilet.
Thank you for pointing out that scenario. I've added the following code with an exit to ensure that doesn't happen.
[ $STATUS -ne 0 ] && yaf-splash -font "8x16" -outline 0 -margin 4 -bg orange -text "FAILURE! $P could not unmount - Perhaps files are still in use or no directory was specified" && exit