Richard Compton said:
I forget whether the bridge was rebuilt before or after the second pilot. I'd have to look at the episodes.
OK, this is starting to make more sense. In the Solow/Justman book "Inside Star Trek", they talk about how the bridge was moved from the Desilu Culver City studio to the one in Hollywood. They took the opportunity to make the set completely wild by cutting it apart and rebuilding with lighter weight materials. Like you Richard, I also forget when this took place. Also, this view was used in the first production episode "The Corbomite Manuever", but it was aired as the 10th episode. But since these are effects shots, they could have been processed at any point between.
Also, the positioning of the rails could be different because the wild sections weren't always placed together exactly the same way (as discussed in the bridge blueprint thread). So the placement could have been done accidently, or on purpose to provide perspective.
I suppose this could have been just another instance where time and money constraints always played a part in production, so no big deal today if something doesn't quite look right. Like they say in the "Art of Star Trek", nobody expected that 40 years later fans would be dissecting and examining the episodes with such "enthusiasim".