Report Open vs Closed Work Items only works with un-archived iterations

Hi, all

We've just started looking at predefined RTC reports and particularly the Open vs Closed Work Items report

We have noticed that we are not getting truly consistent numbers each month we run it. It seems that when we delete (archive) an iteration (which we like to do to prevent accidental assignment of work items to the wrong iteration after it has been completed), the report will not include any stats for any work items Planned For the archived iteration

Looking at the report's parameters, it only has the 'visible' iterations listed

Does anyone else have this problem and have any suggestions on how to overcome this? (apart from not archiving iterations)

Thanks

David