PN:Question on setup option

There is a setup option called Extend Index Rent Terms Upon Lease Extension.  Possible answers are yes or no.  I assumed that if answered yes then when I extend a lease via either extending the termination date or via the month to month status that it would extend them.  If the answer was No then PN would do nothing to the increase.  I have tested this and find the same behavior irrespective of how this is set.  Can someone tell me what this is suppose to do?  If it is broken I will open an SR.  Thanks.