I know what they mean, because I have the same issue on my work pc (but not at home). I forgot it happens because the personal userstyle I'm using includes CSS to fix this issue entirely.
@speck get yourself Stylus if you don't have it already and try this CSS which works perfectly for me:
div.more:not(:nth-child(1 of .more)) {
display: none;
}
Can't guarantee it works with kbin's built in custom CSS functionality, as that one seems to filter out some selectors (no logic behind which).
@shazbot
Basically, what happens without that CSS is that
Clicking the bar once scrolls me down a bit but otherwise does absolutely nothing.
Clicking the bar again turns the arrow upwards and spawns a new bar above the existing one.
Clicking the upper bar repeats step 1.
Clicking the upper bar again turns the arrow upwards but doesn't spawn another bar, nor does it do anything else.
Clicking the lower bar removes the upper one again and turns the arrow back downwards.
At no point is the comment ever expanded. When OP says it obscures text, that's just the default state where only x lines of the comment are shown and the bar covers the last line(s). The issue is the comment can't be expanded, so it keeps obscuring the text even when clicked as nothing actually moves.
Looking at the HTML source, I can see five instances of the bar existing at once on the same comment.
I tested just now to turn off my scripts one by one and KES was the culprit. Disabling it fixed the issue. I'll try checking which feature is causing it.