Problem
POs are being counted towards Job Costing, causing duplicate items and inflated costs. You want to attach POs to jobs without affecting Job Costing.
Solution
Attach PO to a job
Search for the job that you want to attach a PO to.
Click Job Actions and select Purchase Order.

Fill out the necessary information for the PO.
When finalizing the PO, select No when asked if you want to copy the items to the invoice.
Note: This only occurs if you have the Option to add inventory items to invoices setting enabled in the Inventory Configuration settings screen (Settings > Inventory > Configuration).
Click Save to attach the PO to the job.
Remove Duplicate Materials from Invoice
To remove duplicate materials from the invoice, navigate to the job's invoice and click the small X icon next to the items you want to remove.
The invoice's costs are now zero costs while the PO now contains the costs, so there is no double costing.