I remember a similar incident during Match of the Day a few years ago in the early days of the new playout centre. As I understand it, they move the channels between playout 'suites' late at night to bring them into the same playout suite and there's potential there for a switching error
That was unedited footage of the Cricket World Cup being fed back to the Beeb and put out during Match of the Day in error.
There's been a couple on Sky Sports, specifically PremPlus when that was still going. I remember a Saturday 5.15 game where, early on, it switched to footage of a goal from one of the 3pm kick-offs (which hadn't been televised yet of course) being replayed several times from several different angles, presumably being edited for Football First. Also one Sunday afternoon match was replaced for a minute or two by what was presumably a Sky News crew waiting around by a doorway for someone to come out. Nobody watched PremPlus though, so nobody noticed.