Reversal of Overhead

Hi

I want to reverse (KGI2) overheads posted in April for a particular Prod order, but not able to do it so, if i try in Test run in April after opening in transaction in OKp1 i am getting value

Is this std behavior where i cannot reverse the April posting in June. In this case how to reverse the OH posted?

There are few threads relating to this, but no clear solutions.