Negative acceleration basically means that the rotation in-game is shorter than in should be based on either settings, movement speed or both. So say you want a 360 distance of 10 inches and if you move the mouse slowly you get 10 inches, but if you move very quickly you might get for instance 12 inches. It might also always be longer regardless of movement speed due to other factors. This means the game is either missing some reports from the mouse, or registering them as shorter than they should be. Reducing report rate in the mouse driver often helps with this issues, as quite a lot of games struggle with 1000 Hz (reports are coming too fast for the game to process). I'm not sure if this is the issue with this game in particular though, but it's worth a shot.