Other mistake: Dunbar has to race back to the fort in the middle of having a shave. The amount of soap on his face alters shot to shot.
Other mistake: At the beginning after Dunbar leaves the surgery area, he walks up to fence where a soldier is lying down. Next to him is an apple with the grocery sticker on it. (04:49:00)
Answer: He was mentally disturbed and was depressed about being assigned to a "dead end" post with no chance at advancement. Dunbar, the hero, choosing to be assigned to the frontier, just pushed the poor soul over the edge.
Mark English
In a word, the disease syphilis. The urinary tract problems and the Insanity are possible side effects.
What are you basing this on? What in the movie indicates that he has syphilis?