Related stories: "unit tests fail when run in Australia" [1] and "the case of the 500-mile email" [2]. There is a whole GitHub repository dedicated to some very interesting debugging stories [3].

[1] https://github.com/angular/angular.js/issues/5017

[2] http://www.ibiblio.org/harris/500milemail.html

[3] https://github.com/danluu/debugging-stories