Yes, it happens to everyone from time to time. Save whatever game you're playing, close out the Game window, and then open a new game window and resume your game. The jerkiness of the swing bar should be resolved, at least for awhile.
This problem, and other hesitation-type issues, are inherent in most flash games you'll play, as they have a tendency to become a memory sink when played for long periods of time. I generally try to reload my game window after about 4 rounds, that way I keep the issue from manifesting, for the most part.