Acumatica – Detail Record Not using Auto-Numbered Field of Master Record

I have a maintenance form in Acumatica 2020R2 that has a master-detail relationship between a form and two tab items that contain grids. I have the ID of the form auto-numbering, and the detail records use this ID with the PXParentAttribute. The form auto-numbers and saves to the database with the correct ID, but the detail records are saving to the database with the initial placeholder <NEW> instead of the auto-number.