Well, while it's far from an international incident, I would say it is a bit lazy... if you want to depict England on screen but you can't sort out certain details, that's lazy film making. Would Spielberg screw that up?
Apparently Mr. Spielberg made a whole bunch of real
historical mistakes it his latest masterpiece Lincoln
I ain't worried about an upside down flag in a movie about future fiction.
a Pulitzer Prize-winning historian of the period, claims in a letter to the New York Times that the movie “grossly exaggerates” its main points about the choices at stake in the passage of the Thirteenth Amendment (November 26, 2012). Kate Masur (Northwestern University) accuses the film of oversimplifying the role of blacks in abolition and dismisses the effort as “an opportunity squandered” in an op-ed for the New York Times (November 12, 2012). Harold Holzer, co-chair of the Abraham Lincoln Bicentennial Foundation and author of more than 40 books, served as a consultant to the film and praises it but also observes that there is “no shortage of small historical bloopers in the movie”