If an item is both overdue and lost, renewal of that item will generate fines. This behavior is inconsistent with the behavior of the fines cron, which explicitly excludes lost items from fines. I expect there are libraries that prefer the current behavior but also libraries that would rather not generate overdue fines on renewal of lost items. So perhaps a system preference is in order? Do/Don't charge fines on renewal of lost items?
Is the item still lost after renewal? I seem to remember another bug about this.