Resolution Time report shows inaccurate open time

The "Resolution Time" report is purported to show the "average time taken to resolve issues." It appears to use the resolved date field to compute the open time. When an issue is marked as resolved; however, when the issue is closed (which may happen much later in the lifecycle) the resolved date field is updated with the close date. This causes the resolution time report to show open-to-closed deltas rather than open-to-resolved.