There are tons and tons of them if you look - although Max would still like to know of more - where the local knowledge of London's Underground stations isn't quite up to scratch and we get wonderful typos, stations left off or removed, colours of lines all over the place and other weird anomolies. If you spend an afternoon in Stanfords flicking through international guide books to London, and looking for the Tube map, you'll see what he means.
However, thanks to Jon Choo who was also at the talk, I've found my first online version. Take a look at just a section of the map above from Subwaynavigator a French website, and try to spot the mistakes.
I'm no expert in the Tube Map, but I've spotted three errors in just that section alone. And if you're wondering what that strange orange line is, it's the Central Line and I really haven't messed with the colours! Enjoy and, no prizes for spotting the other mistakes, just the satisfaction of knowing that you're right!