never had an issue. quite the opposite once on the old 772 JFK-LHR two summers ago. i had a shoulder injury and was in F, my boyfriend at the time was in coach.

i needed him to board with me and lift my bag into the overhead.

doors close and the purser who saw me board went back to coach to grab my boyfriend and seat him next to me in F. talk about luck!

ps: it has never worked again since