Hi Graham, There should not be any duplicate postings in CO. In this instance, the cost center postings would be considered as Statistical postings. You can see the same in COSP table with value type -11. This will NOT be settled further to any other cost object. PM order postings are real posting and further settlement can be done from there. This scenario should not create any issue in CO module. I hope you are finally settling the PM orders to plant specific cost centers. You should be good.
Hope this helps.
Regards,
Srinath