Continuity mistake: During the entire battle the ground is sticky mud. When the French cavalry charge however the ground is dry, so dry there is dust coming from the horses' hooves as they gallop.
Continuity mistake: When Ponsonby is killed by lancers, his horse struggles in the mud. One of the shots shows a dark brown horse's legs getting stuck in the mud. All other shots show a grey horse.
Answer: I think the film's dramatisation of this particular incident, when the French army defected from the restored Bourbon royal family back to the Emperor Napoleon might owe something to the painting NAPOLEON RETURNED painted in 1818 by Charles Steuben (also called Charles De Steuben and Karl Steuben) a German who became a nationalised (and patriotic) Frenchman https://commons.wikimedia.org/wiki/File:Napoleon_returned.jpg.
Rob Halliday