New glitch in the right-side thread scroll bar?

I’m seeing a glitch in the right-side scroll bar. It’s happened several times, but I’ve only noticed it recently.

Background: When viewing a thread, the scroll bar that appears to the right of the thread shows with the current post number along with the scroll bar itself. At the bottom is the time of the most recent post, which is clickable. BUT: When composing a reply, the thread as shown in the upper half of the screen shows a very abbreviated version, showing only a box with the current and last post number.

Now sometimes, when I finish the post and submit it, and the full screen reverts to showing the thread with the new post, the full scroll bar does not re-appear, but instead only the very abbreviated version (with the box with the current/last post number) remains.

Refreshing the page fixes it.

Now, I’ll admit my computer is old and glitchy and just maybe it’s just a local quirk. Is anybody else seeing this?

ETA: I also just noticed, in composing the above post, that the display looks different when composing an OP, from what I remember seeing in my (infrequent) prior OPs. Now, instead of a quarter-screen compose box and quarter-screen preview box, both are enlarged to a half-screen (there being no prior posts to display in the upper half of the screen). This seems like a perfectly sensible recent change, if in fact it is recent. Is it possible that the above-mentioned quirk is related to this?

Bumping this. Anybody else seeing this glitch? Only me?