Resource Spread

My settings for Earned Value are Planned Values with Current Dates. However, when viewing the resource assignments, the Resource Spread is using the Activity Planned dates and not the Activity dates (Actual Dates). This only happens on Activities that have started or completed. understandable as it is expected that these Planned Dates are likely to be different. Is P6 therefore set up to only show accurate data for Budgeted Values on unstarted activities. Or, what other settings are there in P6 that may cause this anomaly. Thank you.