"but I use a "work log" (a LibreOffice document) to compose in, as a general rule."

That's a good rule to follow.

"It seems that the spinning behavior is worse when you're looking at a feed and left-click a link, which causes it to appear "above" the feed"

I have noticed this as well. I've been opening comments into their own individual windows, but that is labor-intensive.

"Then I switched to the tab and saw that two of those upvotes had been recorded. I made the third, and then started writing this comment. "

Everything you describe here I've seen as well.