Just after Mrs. Miniver hands the German pilot a bottle of milk to drink, spilled milk appears all over his coat. The milk subsequently disappears and reappears on the coat several times between shots.
When Mrs. Miniver is rushing across the crowded sidewalks, the number and size of boxes she is carrying changes.
In the first church service scene, a woman who is in front of the Miniver family begins sobbing with her face buried in her hands. In the next scene from a greater distance, the woman is standing and no longer crying.
In the radio broadcast of Lord Haw Haw, he mentions the fall of France. Then a day or so later, the boats are called out for the Dunkirk rescue mission (Operation Dynamo). France did not fall until 2 weeks after Dunkirk.
Mr. Ballard's rose would not have survived the number of months over which the course of the story takes place until the flower show.
The double-decker bus seen in the opening sequence is not a British bus at all, nor was it a real a double-decker bus. An American bus was used, with a false upper deck grafted onto it. The American-style passenger door can be seen on the right-hand side in the bus's first appearance; a real London Transport bus would have had its door on the left-hand side.
The Minivers' telephones are obviously American sets.
When Mr. Miniver comes out of his bomb shelter for a smoke, his pipe is upside down. How did the tobacco and hot ashes stay in the pipe while upside down. Was this to hide the smoke from the enemy.
When the German pilot is moving through the kitchen door, his mouth is moving and he is clearly saying something, but there is no sound. This may be because the scene was reshot a number of times.
After Mrs. Miniver congratulates Ballard on the win, he says, "It's your rose, ma'am," but his lips don't match the words.
When Walter Pidgeon hops into bed in his pajamas after returning from Dunkirk, a part of his anatomy is briefly visible. This was missed in editing and remains in the film to this day.
Early in the movie, right after Mrs. Miniver gets off the bus and is rushing up the sidewalk, the camera's shadow falls across her face.
When Vin and Carol are returning from their honeymoon on the train, the reflection of a crew member, equipment, and a small desk can be seen in the windowpane to the left of the couple.
(at around 20 mins) Clem drives his new car around his village on the right-hand side of the road, not on the left as is done in England.
(at around 25 mins) Clem asks for "ham and eggs" for breakfast, an expression far more suited to the US. "Bacon and eggs," however, is synonymous with an English breakfast.