This is a very minor polish issue that's been around forever, but if you click on a keyframe in the timeline docker and drag it around like crazy it will lag behind, slowly following the whatever path you've taken with your mouse while falling further and further behind. It's pretty cool. :) We probably need to somehow optimize the way drag-and-drop works with timeline frames. (We probably also need to make it so that it doesn't scrub the timeline while drag-dropping. That may be part of the issue or a separate problem. I'm not quite sure.)
I can't tell if this was an upstream issue that's now fixed, or if my new CPU is just overpowering the problem to the point where it's not noticeable anymore, but I can no longer reproduce this one and so I'm closing it for now. As an aside, the last time I tested it I found that this is not specific to the Animation Timeline Docker, but can also happen with drag-and-drop elements of other dockers, including the Layers Docker. That leads me to believe that, if there is still a problem, it's probably just some unoptimized drag-and-drop code upstream.