Revealing mistake: Every time Colter finds the bomb, the cell phone used as the detonator, is running a Adobe Flash movie named "HISTORY.swf" on its screen. The Adobe Flash Player logo is visible in it. When he removes it the first time and tries to call back the bomber, it's nothing but a Flash animation sequence playing on this mobile. (At about 01:11:20) Finally he finds the secondary mobile at the back of the bomb, and this too has a HISTORY.swf playing in it. (00:15:30 - 00:55:00)
Source Code (2011)
1 revealing mistake
Directed by: Duncan Jones
Starring: Jake Gyllenhaal, Vera Farmiga, Jeffrey Wright, Michelle Monaghan
Audio problem: This scene is repeated multiple times in the movie: usually when the main character enters the "source code" the scene begins by panning over a small pond showing a Canada goose taking flight. However the sound editor makes the mistake of dubbing in a recording of a hen mallard duck.
Colter Stevens: Tell me everything gonna be okay.
Christina Warren: Everything's gonna be okay.
Trivia: Derek Frost has 2 totally different driver's licenses. All personal data is different.
Answer: He died in the train bombing along with all the other passengers. If you're asking what happened to the real Sean Fentress in the alternate time line created at the end of the movie, Colter took over his body and continued to live the life that Fentress had been living.
Casual Person