DHCP IP ranges and Scope options wiped out

This morning we came in to find that IP ranges and scope
options had been wiped out. We could not find an entry in
the DHCP logs or in the event logs. All I found was this:

"There were some orphaned entries deleted in the
configuration due to the deletion of a class or option
definition. Please recheck the server configuration."

Has anyone ever seen this problem before? Does anyone
know what causes it?

Also, how often does the database cleanup occur? Could
that have caused this problem?