What would cause a one time override to be deleted from the F0709 upon payroll reset?

I have a client who is processing an adjustment payroll due to monthly benefits being collected twice in a payroll month when they should only have been collected once.  They are trying to process an adjustment payroll to back those out.  They have the benefit DBA's and amounts in a spreadsheet and upload them into the P07OTO1 program.  The Deduction/Benefit Override Code = MP.  When they reset prepayroll the DBA's are being deleted by the system so they have to be uploaded again.  I am not entirely sure if they are all deleted.  Can someone explain why this is potentially