I’m not sure if this began occurring with the new update or prior, but now when I scroll down a longer topic, the post number on the timeline scroller remains the same until I click my left mouse button or wait for what seems like an extended length of time.
Additionally, when I scroll up to reach the top of the post, the timeline scroller overlaps my global notice (as seen in the screenshot below).
And here’s a GIF of the bug caught in the act (you can see it snaps back once I click)!
What’s the repro here on meta? There’s a number of CSS customizations that could affect this, so I’d like to rule them out by having a repro here on meta.
Looks like it doesn’t happen here! I’ll crawl through my CSS and see what I’ve done to myself. Thanks, Jeff!
Any mucking with height of the page is particularly risky and we’ve seen customers get themselves into trouble with that.
As bizarre as it sounds, turns out that after I reset my PC and finished a Windows Update, it pretty much works like normal again. I also went through and disabled all my CSS, then retested it by enabling them one-by-one and seeing if there was one that set it off, and they all seemed to not affect it.
Thanks for the assistance; we can consider this case closed for now! 
