When Van Gogh is at the window, after he cuts his left ear off, his right ear is bandaged.
At Arles, when Paul Gauguin is explaining his philosophy, Vincent mistakes him for Theo saying "but Theo, err Paul..." However, this is in the script. The whole point of the line is that Van Gogh views his conversation with Gauguin as nothing more than an extension of talks he's had with Theo since childhood.
For some inexplicable reason Vincent's letters to Theo are narrated by someone other than Kirk Douglas, and uses a distinct English accent. The letters are being narrated by James Donald (Theo), who is the one reading them.
While a strong wind lashes Vincent van Gogh and Paul Gauguin in a Brittany vineyard, blowing over their easels and causing Gauguin to call it a "gale", the trees in the background are absolutely still.
Camera shadow falls across Ducrucq as Van Gogh finds him dead.