Sequence / rendered animation is different to viewport animation.

Hi,
Curious if anyone has issues when rendering character animation (using the puppet tools) and the animation is different to what you see in the view-port? I'm rendering a 100 frame sequence and there's a lot of differences in how the body moves .. in the view-port its smooth and nice, as i expected, however in the rendered sequence, the body motion is quite erratic. For example the say the arm, moves very slowly, then suddenly jumps to the target position within a few frames .. where as in the viewport, its a smooth arm movement.
Thanks, Marie