That's what I thought, and that is what I usually see.
However, sometimes I will see the "red Yes" in my Watched forum list.
Then I go into the forum and see "black dashes" above The "red Yes" in the far-left column.
If there was a new post since I was last in the forum, shouldn't that time stamp be more recent than any thread with two black dashes?
I assume that I'm confused rather than the feature acting erratically, now that I'm using FireFox almost exclusively.