The DL systems get confused. DL uses G for PS on its A350 and soon to be 777 planes. Thus since you have to book using the DL codeshare the system sees G and thinks its PE. It doesnt understand that G is PS only on actual DL metal flights. Badically its an error that DL IT needs to fix, but that doesnt actually really cause an issue, just confusion. Youre in UC if in G on a VS flight.