I have also read that it was possibly a deliberate joke.
Which this can’t be. In one of the Highlander films McLeod arrives at Newark airport and you can clearly see a sign saying Bienvenu à Montréal on the wall.
The James Bond episode of “Top Gear” shed light on this. The exit was shot first and someone discovered that the entrance wasn’t shot until production moved to England. Guy Hamilton wasn’t available for the entrance shoot and whoever was in charge just set it up wrong. Nobody noticed until the editing was finished.
Just watched Down in the Valley the other day, and Edward Norton’s facial hair probably could have been paid a little closer attention, especially toward the end of the film.
Norton’s character and his “hostage” are on the lam, just had a shootout in the woods in the middle of the night, then ran off into the dark, not apparently being followed by the wounded pursuers. Norton had a handlebar moustache at this point.
Next we are shown: Norton wakes up in an abandoned building the next day and is clean-shaven!
I love in Geena Davis’s “The Long Kiss Goodnight” when they’re walking along the street in “New Jersey” and you can clearly see the very unique Honest Ed’s sign in Toronto behind them.
Am I crazy, or did anyone else notice in Skyfall that Bond’s chest scar, from getting shot in the opening sequence, either moves around on his chest, or is non-existent? I think there’s a scene in the Turkish beach resort where he takes his shirt off and there’s either no scar or it’s on the wrong side of his chest. Whether the goof actually exists or not, my GF and I remember being really bugged by it in the theater.
If you watch any episode of the Brady Bunch you will notice that whenever the famous screen door to the backyard is opened it never has glass, it is just the frame!
The cameras of the day would show the glare/reflection and therefore all glass had to be removed (same effect in scenes where the camera is supposed to be looking through a car window.
I only know this because Grandma has my 2 year old hooked on the Bunch and I have been watching Waaaaaaay too much of that show lately! 
And just yesterday, I took a train to the airport. (A MARTA train, to the ATL airport.)
In the episode of “Murder, She Wrote” set in Moscow in the dead of winter, a limo pulls up with its rear window open; after the guy in the back seat finishes conferring with his colleague in the street, the window goes up and we clearly see the reflection of the camera and crew about four feet away. It is REALLY, REALLY obvious (at first, I thought they had done it deliberately for some reason)!
In one of the Naked Gun movies (the first, I think), they’re supposed to be in Washington, DC, and the outdoor scenes regularly show palm trees and the like; in the big shootout on the roof of the hotel, there’s a huge sign in the background that says “VAN NUYS WAREHOUSE.”
Granted, Naked Gun was supposed to be farcical, but still… :rolleyes:
The film was Presumed Innocent (1990). I remember seeing that in the theater and it immediately jumped out at me because I owned the same model microcassette recorder.
My all-time favorite is from the final fight scene in Bad Boys (the 1983 film with Sean Penn and Esai Morales). Here’s a clip (details in spoiler).
The cameraman shooting the fight from the opposite angle is plainly visible in the frame.
But that’s not a goof, just “movie magic”.
I can’t recall the name of the movie where I saw a boom mike appear in the top of the screen. Some big historical pic. The scene was set around a breakfast table or something, and the boom mike drops into frame. I was trying to figure out if they were having someone film them at home for some tv special or something, before I realized it wasn’t supposed to be there. Really jarring. I think the picture was slightly misframed on the theater screen, sitting a bit low.
Roger Ebert has discussed boom mikes in his column many times. The reason they appear sometimes in movie theaters is that the projectionist didn’t frame the film correctly. The overall image is larger than what’s intended to be shown and the projectionist is expected to cut off the extra.
Ebert would write about that in his Answer Man column every few months. What happens is the movie is not properly framed at the theater. There’s a space all around the screen that is not supposed to be seen by the viewer. I remember seeing this happen in the Karate Kid once and wondering how the heck that got in there and then never seeing it again on subsequent viewings.
The same thing happened in Silence of the Lambs (at the start of the elevator scene) and Married to the Mob (when Michele Pfeiffer was sunbathing on her patio). I saw these in cinemas in Czechoslovakia and Russia, respectively, so it’s possible they were cheap prints cobbled together from outtakes for overseas distribution, but the effect was still (as you say) jarring!
(Were the prints shown in the US and elsewhere any different? To this day, I still don’t know!)
EDIT: Just read the above posts; sounds like my question is answered!
I don’t know if this counts as a goof, but Rumble in the Bronx was actually filmed in Vancouver, and in several scenes you can see lovely picturesque mountains in the background.
In Jackie Chan’s “Rumble in the Bronx” - he gives the kid a Game Boy type game (I think it was Sega’s version) - the kid immediately starts playing it, but there is no game cartridge in it.
Just like the streets of London in the first Austin Powers movie! 
Not saying it can’t be done, but in a movie where a person is going from NYC to London it makes better sense to have your tearful going-away scene set on a piece of transportation that will actually get one there…
The Transformers movies can fill the universe with lists of bloopers, but my favorite involved the second movie, when Shia and Megan run into the Smithsonian Air and Space museum in downtown Washington (some argue it’s another museum in Manassas, but the problem remains the same.) They meet with another transformer, then all hell breaks loose whereupon Shia and Megan run out of the Smithsonian…
… to find themselves in an airplane graveyard, over a thousand miles away. No city, just plains with mountains in the background.
Truly… WTF?
The big battle at the start of Gladiator. The headless horseman is using stirrups, which were not in use at that time by Romans.