Firming a planned purchase order receives XDS error

I have XDS setup with a constraint on site for the PurchTable based on the users site. Users have had no issues with this in regards to creating new purchase orders. However, we are running into an issue where it won't let the same users Firm a planned purchase order. We get the error: "Cannot create a record in Purchase orders (PurchTable). Security policy permission denied."

I can confirm this is an XDS issue because if I disable the Security policy then there's no issue with firming. See attached for screen shots of the XDS setup. Does anyone have an ideas as to why it would do this?

Thanks!