(experienced this only once too a few day ago, not bothered me much more but, may be this could help: ) i suspect this to be related to a revert in speed value as it happen at the exact same time the navball revert. i mean the game act if you're doing a huge accelleration to simulate the fact that speed is remaining constant and revert in the coordinate system (not sure it's well explained but, probably some clue around this part within the code, and how some other sub routine deal with this fictive acceleration due to coordinates references changes)