This is the same issue as
But in Apps10 Aurena instead.
There is an issue when working with the Quick PO Registration. The No Part Lines do not stay connected to project when you convert it to PO. The connection does stay for the Part Lines.
The No Part Lines connection does show on Quick Purchase Order Registration screen, but when the PO is created, the Project Connection disappears.
This has been tested with multiple projects, POs, and in different environments.
There is a fix for cloud, but is there a fix for Apps10?