SilverWook said:
My favorite open matte "blooper" is the scene in Bachelor Party where a character wrapped up in bedsheets falls out a window. Two very visible stagehands are at the bottom of the screen to catch the actor.
One of mine, I don't know why, is in The Mothman Prophecies, there's a scene in the fullscreen version where the main character's hands are bloody for no reason. Probably from a deleted scene.