As the stairs turn the 180 degrees at the top and the bottom they are turning on a much smaller roller or gear than the hand rails. In order for the hand rails to keep up exactly as the turns come at the top and bottom of their travel, they would have to move much, much faster than the stair treads, then, as they treads and the handrails start their trip up (or down), the handrails would be traveling much faster than the treads. What you are experiencing is a compromise. No, you are not imagining it, the handrails are actually moving slower than the treads. Welcome to the world of aviation. Many things to observe about this job besides flying!