If you need the file, here.
The bug: I animated the mainmover bone’s rotation (the one that sticks out of his ass) and changed the IPO curve type to cyclic extrapolation. Watch the atrocities which follow. The bone slows and comes to a stop though the curve shows it should continue.
From then on, all animation is impossible. After creating this bug, you can’t fix it by changing the curve back to constant and bezier, and moving the timeline back and forth, you can definitely see it’s a bug. Move it forward, it will play the animation (incorrectly), move it back, and it won’t move at all until it reaches frame 1. This really messes up the animation process.