Happened to me for the first time at SFO last week (Sunday), except I was #1 on the list with 2 seats open. Being a 757, they started cattle-call about 45 minutes out. They told me to wait at the gate until the 30-min mark when they can officially release the seats for battlefields. So I watched as all of coach boarded and took my overhead space. Luckily, though, my UG cleared and FC overhead was not full. I did, however, get a nasty glare from the pax in 5D (I was in 4D) as I stowed my backpack above my seat. I, too, was returning from China. Well, Singapore, Cambodia, Thailand, Malaysia, China, and Hong Kong. So, at least the UG was very appreciated by me.