I'll have to look that up. The article I read says that icing rules revert to normal when the penalty is over, not when they're back to five skaters.
I believe this is true unless they changed the rules. I remember a few times where teams iced the puck just after the whistle blew and they got called for it. Of course it may be that their player was in the box and had come out. I don't recall every seeing a case where the penalty ended and a player didn't come out of the box immediately. I would like to have seen that game.