Cost method 08 updated on Vendors Return

Hi All

We have some (not massive but a few) issues where because cost method 08 (latest purchase price)   is updating
dynamically on a PO receipt (OI Type) and voucher match it is updating on purchase returns.

Is it possible to exclude this  OI order types from this update? 

This causes us issues where for example we raise an voucher months/years later and they send them back at an old price OR
  where the supplier says they aren’t giving us back a credit for whatever reason as this updates the last price paid (P0411/P4314) programs.

Thanks in advance for your help