I have used it in Battle revolution and it goes away after about 5 turns but on Gen V PO it doesn't seem to until The pokemon faints/switches. So did it change in Gen V or is it just PO loving Whismicott?
In the Fifth Generation of Pokemon The move Leech Seed Will last for an infinite amount of time, Unless your opponent Faints, Switches, or Uses a Move like Rapid Spin to get rid of it.