A process is required to remove orphaned records from the NCM database (i.e. interface records that do not have nodes associated, policycacherecords that have no nodes etc).
Refer to Re: Unmatched Interface Records for why I think this needs to be treated as a bug rather than a feature request.
I agree, this is a bug. We're looking at this in our next dev cycle. For internal folks, this is being tracked as #4259