Happens all the time at Woking for down services on Platform 4 and 5. There is a double crossover at the London End of Woking. As services can be running so close together, if anything is delayed there is a chance they will play musical platforms.
On a dozen occasions, if services are running late Ive see trains change platforms literally as they come into the station, causing everyone to mad dash over the bridge. This causes chaos as a lot of the time people are standing at certain places all along the platform to get on at certain points of the train. This is really bad luck for anyone hoping to get on at the front of a 12-car as the footbridge is located roughly around the back 2 or 3 coaches of these sets.
Still it gets worse though. On more than one occasion the platform has been changed twice in less than 5 minutes. A departure from platform 5, changes to platform 4. Then, and only once EVERYONE has moved to platform 4, do they announce - oops sorry, it will be platform 5 again, and everyone has to walk back!
Its almost the norm now that if services are running late, hang around the bottom of the stairs to the bridge until you are certain the train you want is going to stop at the platform you're on.