Earliest MD Change date being updated during time eval

Hi

We upgraded to ECC6 on Sept 8th 2008 and we have three payroll period parameters. All Monthly employees use period parameter 01 and weekly period parameter 03.

However, payroll area W1 used a custom period parameter 99 because the week started Sunday and not Monday as with all other weekly employees.

Since the upgrade, W1 payroll has been recalculating from Sept 9th for every employee in the payroll area even though there is no retroactivity.

I have noticed that prior to running time evaluation, the Earliest MD change date in PU03 is correct, but somehow during time eval. this date is changed to 09.09.2008 for all employees in the payroll area.

What would cause this to happen each time and how can I correct it?