service order with ref to PR

hi,

we have activated PR mandetory for PO.

here for service PO i am facing some problem, please help.

if the service PR is having one main line item and 3 sub line item, while copying the same to PO, it will copy, and along with this 3 sub line items, i can add multiple sub line items, which is agains principle pr mandetory for po and po qty should not exceed the PR qty.

how the same can be controlled.

at the same time while copying the PR for creating the PO, the account assignment tab at item level gets grey, that means, i cant change the account asignments at item level.(order, asset , cost centre...etc)