Other mistake: Johnny Brown is serenading Molly in the meadow as she sits up on the branch of a tree. In shots where we are looking down on Johnny (from over Molly's shoulder), the shadow of the canopy that protects the actors from the sun can be seen as a perfectly straight line on the ground, behind Johnny. The shaded/unshaded areas move as the canopy shifts in the breeze.
Other mistake: When Eliza throws the slippers at Higgins, one bounces off him and falls in the area of the doorway and the other lands in the middle of the hall. One slipper is seen in the hall in two different scenes, then when Higgins goes to pick them up they are both together in the hall.
Other mistake: When Charles is buying the car, he says to the dealer, who knows Charles very well, that the phone should be on the left, and the dealer, who knows what's coming, says of course, and agrees that it must be done before delivery tonight. When the car arrives, the phone is still on the right.