The clone circ rules widget on the circ rules page unconditionally deletes the target library's existing rules and replaces them with copies of the rules from the source library.  Consequently, if the clone rule button is accidentally clicked, a lot of configuration work can be destroyed in an instant.

To avoid this:

* there should *always* be a required confirmation step, whether the clone-rules.pl script is accessed directly or via the smart-rules.pl page
* even better, a backup copy of the previous version of the target library's rules could be made

The library who ran into this bug had tried cloning the rules form a different library because they thought that would be a way to copy over that library's rules and add them to the rules that the target library had previously entered -- that kind of cloning-via-merge feature also seems like a good idea, in fact.