Revealing mistake: In the scene on Christmas morning when the Bumpus' dogs run in and eat the turkey, during the shot of the dad sitting in the chair reading the comics, one of the dogs bumps the camera and jostles it a little bit.
Revealing mistake: When Ralphie is walking along after getting the C+ on his theme, he gets hit with a "snowball sandwich." if you look closely at his face and eyes, you can see that he has his eyes closed in expectation of getting hit.
Revealing mistake: One shot of the family opening the Christmas presents is from above; if you look quickly near the top of the screen you can see the ceiling cut away and even shadows moving on this area - obviously a set piece.
Revealing mistake: The wind up tank in the toy store window can't possibly be a continual display. Clearly a production assistant wound up and released the tank for the shot. It's not a toy that would be moving with the other display items.
Revealing mistake: When Dad gets the bowling ball, it's already drilled, and obviously not for him. Watch how he holds it and puts it down. The holes look very small.
Revealing mistake: When they close up on the boys at the flagpole you can see what is probably a pole support bar going down at 45° from the flag pole. Though looking too straight for flexible tubing, this could alternatively be an air suction tube that was used in holding Flick's tongue to the pole.
Revealing mistake: After Ralphie's dad loosens the first corner of the crate, it's very obvious the other corners were deliberately left unfastened to make it easier to remove the lid on camera.
Answer: It's most likely a reference to the twin-bed movie standards from the time in which the movie takes place (late '30s to early '40s).