I had a suspicion about this a few months ago. I was headed from DEN to MSP on DL and it was arriving a hour late. There was a large tour group connecting to CDG (AF codeshare I think). The MSP - CDG flight was the same flight number. They made a heroic announcement they were "holding the plane" for that group and they should deplane first. I figured they actually couldn't leave the gate until the flight sharing the same number landed. Maybe I'm just a cynic...