I did it on the phone (to DXB) twice, for several sectors. The one time I did it in the lounge was more a case of "Not available now. Come back in an hour to see if we can process your upgrade then. I'll make a note to hold it for you if it becomes available."

The ones I did on the phone all showed in MMB for weeks, but none of them ever came through. Although I did get a cash upgrade email and then an opup on one.