No of course it wasn't intentional but why change something that is inherent to the original at the time it was made?
Good point. The more I think about the more this is how I remember seeing it on TV during the 70s and 80s; the credits are shown letterboxed as per the DVD and bluray, but then the image is corrected (squeezed) after the opening plane crash sequence.
As to why? Well, ... I get the sense that the producers and crew overlooked it because perhaps they felt the director wanted this as some kind of artistic flare for the film, when I think in reality it was just a simple error during production. So ... for dudes like me it's one of those "hey look, that's a mistake" kind of thing.
I mean, it's not that big a deal, but one wonders if perhaps the production team (surviving members at least) wouldn't want it corrected.
I guess maybe it's a non-issue for most people.